Polymeric interlayers and multiple layer panels made therefrom exhibiting enhanced properties and performance

ABSTRACT

Polymeric interlayers for use in making multiple layer panels having a unique balance of properties are provided. Single and multiple layer interlayers according to various embodiments of the present invention can be used to form multiple layer panels that exhibit both enhanced rigidity and improved impact resistance, while still retaining desirable optical performance. Interlayers and multiple layer panels of the present invention may be particularly suitable for use in a wide range of applications, including, for example, in many indoor and outdoor architectural and structural applications.

CROSS REFERENCE TO RELATED APPLICATION(S)

This claims the benefit of U.S. Provisional Patent Application Ser. No.62/352,574, filed Jun. 21, 2016, the entire disclosure of which isincorporated by reference herein.

BACKGROUND 1. Field of the Invention

This disclosure relates to polymeric sheets and, in particular, topolymeric sheets suitable for use as single or multiple layerinterlayers, including those utilized in multiple layer panels.

2. Description of Related Art

Poly(vinyl butyral) (PVB) is often used in the manufacture of polymersheets that can be used as interlayers in multiple layer panels formedby sandwiching the interlayer between two panes of glass. Such laminatedmultiple layer panels are commonly referred to as “safety glass” andhave use in both architectural and automotive applications. One of theprimary functions of the interlayer in a safety glass panel is to absorbenergy resulting from impact to the panel without allowing penetrationof an object through the glass. The interlayer also helps keep the glassbonded when the applied force is sufficient to break the glass in orderto prevent the glass from forming sharp pieces and scattering.Additionally, the interlayer can also provide the laminated panel with ahigher sound insulation rating, reduce ultraviolet (UV) and/or infrared(IR) light transmission through the panel, and enhance its aestheticappeal through the addition of color, textures, etc.

Often, when an interlayer exhibits a desirable property, such asrigidity, it may lack other desirable or important properties, such asimpact resistance or optical clarity. In some applications safety glasspanels may be used as a structural element, but may also be required toimpart aesthetic characteristics to the application. In such cases, anoptimal optical performance, rigidity, and impact resistance is not onlydesirable, but required. Unfortunately, as the rigidity of conventionalinterlayers is increased, the impact resistance of the resulting panelworsens. Similarly, conventional interlayers formulated for enhancedimpact strength often lack necessary rigidity that is required in manyapplications, such as applications requiring excellent structuralsupport properties.

Thus, a need exists for polymeric interlayers that exhibit strength andrigidity, while still providing sufficient impact resistance. Ideally,such interlayers would also exhibit desirable optical properties, suchas low haze and no yellowing. Desirably, these interlayers could be usedin multiple layer panels for a wide range of applications, includingarchitectural applications, and would provide an optimized balance ofstructural, performance, and aesthetic properties.

SUMMARY

One embodiment of the present invention concerns a monolithic interlayercomprising: a single polymer layer comprising at least one poly(vinylacetal) resin and at least one plasticizer, wherein said poly(vinylacetal) resin has a residual hydroxyl content of at least 19 weightpercent, wherein said polymer layer has a plasticizer content of notmore than 30 phr and a glass transition temperature greater than 43° C.

Another embodiment of the present invention concerns a monolithicinterlayer comprising: a single polymer layer comprising at least onepoly(vinyl acetal) resin and at least one plasticizer, wherein at leasttwo of the following criteria (i) through (iii) below are true—(i) saidpoly(vinyl acetal) resin has a residual hydroxyl of at least 19 weightpercent; (ii) said polymer layer has a plasticizer content of less than30 phr; and (iii) said polymer layer has a glass transition temperaturegreater than 43° C., and wherein when said interlayer is laminatedbetween two sheets of glass each having a thickness of 2.3 mm to form alaminate, the laminate has a mean break height, measured according toANSI/SAE Z26.1-1996 at a temperature of 70° F. and an interlayerthickness of 30 mils, of at least 14 feet.

Yet another embodiment of the present invention concerns a monolithicinterlayer comprising: a single polymer layer comprising at least onepoly(vinyl acetal) resin and at least one plasticizer, wherein saidpoly(vinyl acetal) resin has a residual hydroxyl content of at least 24weight percent, wherein said polymer layer has a plasticizer content offrom about 5 to about 30 phr and a glass transition temperature greaterthan 46° C.

DETAILED DESCRIPTION

The present invention relates to polymeric interlayers suitable for usein a variety of applications. When used to form multiple layer panels,including laminated glass panels, interlayers according to variousembodiments of the present invention exhibit an unexpected combinationof enhanced rigidity and good impact performance, while maintainingsuitable optical properties, including low haze and low yellowness. As aresult, multiple layer panels according to embodiments of the presentinvention can be used in a wide variety of applications, includingarchitectural applications, as both structural and aesthetic elements.

As used herein, the term “interlayer” refers to a single or multiplelayer polymer sheet suitable for use in forming a multiple layer panel.Multiple layer panels are typically formed by sandwiching the interlayerbetween two substrates, which can be formed from a rigid material suchas glass, and laminating the assembly to form a multiple layer laminatedpanel. Multiple layer panels may be formed using a single layer ormultiple layer interlayer. As used herein, the terms “single layer” and“monolithic” refer to interlayers formed of one single polymer layer,while the terms “multiple layer” or “multilayer” refer to interlayershaving two or more polymer layers adjacent to and in contact with oneanother. Each polymer layer of an interlayer may include one or morepolymeric resins, optionally combined with one or more plasticizers,which have been formed into a sheet. One or more of the polymer layersmay further include additional additives, although these are notrequired.

The polymeric resin or resins utilized in polymer layers as describedherein may comprise one or more thermoplastic polymer resins. In someembodiments, the thermoplastic resin or resins may be present in thepolymer layer in an amount of at least about 50, at least about 55, atleast about 60, at least about 65, at least about 70, at least about 75,at least about 80, at least about 85, at least about 90, or at leastabout 95 weight percent, based on the total weight of the polymer layer.When two or more resins are present, each may be present in an amount ofat least about 0.5, at least about 1, at least about 2, at least about5, at least about 10, at least about 15, at least about 20, at leastabout 25, at least about 30, at least about 35, at least about 40, atleast about 45, or at least about 50 weight percent, based on the totalweight of the polymer layer.

Examples of suitable thermoplastic polymers can include, but are notlimited to, polyvinyl acetal polymers (PVA) (such as poly(vinyl butyral)(PVB) or poly(vinyl isobutyral), an isomer of poly(vinyl butyral) andalso referred as PVB or PVisoB, aliphatic polyurethanes (PU),poly(ethylene-co-vinyl acetate) (EVA), poly(vinyl chlorides) (PVC),poly(vinylchloride-co-methacrylate), polyethylenes, polyolefins,silicone elastomers, epoxy resins, ethylene acrylate ester copolymers,poly(ethylene-co-butyl acrylate), and acid copolymers such asethylene/carboxylic acid copolymers and its ionomers, derived from anyof the foregoing possible thermoplastic resins, combinations of theforegoing, and the like. Polyurethanes can have different hardnesses. Anexemplary polyurethane polymer has a Shore A hardness less than 85 perASTM D-2240. Examples of polyurethane polymers are AG8451 and AG5050,aliphatic isocyanate polyether based polyurethanes having glasstransition temperatures less than 20° C. (commercially available fromThermedics Inc. of Woburn, Mass.), EVA polymers (or copolymers) cancontain various amounts of vinyl acetate groups. The desirable vinylacetate content is generally from about 10 to about 90 mol %. EVA withlower vinyl acetate content can be used for sound insulation at lowtemperatures. The ethylene/carboxylic acid copolymers are generallypoly(ethylene-co-methacrylic acid) and poly(ethylene-co-acrylic acid)with the carboxylic acid content from 1 to 25 mole %. Ionomers ofethylene/carboxylic acid copolymers can be obtained by partially orfully neutralizing the copolymers with a base, such as the hydroxide ofalkali (sodium for example) and alkaline metals (magnesium for example),ammonia, or other hydroxides of transition metals such as zinc. Examplesof ionomers of that are suitable include Surlyn® ionomers resins(commercially available from DuPont, Wilmington, Del.). In someembodiments, the thermoplastic polymer can be selected from the groupconsisting of poly(vinyl acetal) resins, poly(vinyl chloride),poly(ethylene-co-vinyl) acetates, and polyurethanes, while in otherembodiments, the polymer can comprise one or more poly(vinyl acetal)resins. When an interlayer includes more than one polymer layer, eachlayer may include the same type of thermoplastic polymer resin, or oneor more layers may include at least one different type of resin.Further, although generally described herein with respect to poly(vinylacetal) resins, it should be understood that one or more of the abovepolymers could be included in addition to, or in the place of, thepoly(vinyl acetal) resins described below in accordance with variousembodiments of the present invention.

Thermoplastic polymer resins may be formed by any suitable method. Whenthe thermoplastic polymer resins include poly(vinyl acetal) resins, suchresins may be formed by acetalization of poly(vinyl alcohol) with one ormore aldehydes in the presence of a catalyst according to known methodssuch as, for example, those described in U.S. Pat. Nos. 2,282,057 and2,282,026, as well as Wade, B. 2016, Vinyl Acetal Polymers, Encyclopediaof Polymer Science and Technology. 1-22 (online, copyright 2016 JohnWiley & Sons, Inc.). The resulting poly(vinyl acetal) resins may includeat least about 50, at least about 60, at least about 70, at least about75, at least about 80, at least about 85, or at least about 90 weightpercent of residues of at least one aldehyde, measured according to ASTM1396 as the percent acetalization of the resin. The total amount ofaldehyde residues in a poly(vinyl acetal) resin can be collectivelyreferred to as the acetal content, with the balance of the poly(vinylacetal) resin being residual hydroxyl groups (as vinyl hydroxyl groups)and residual ester groups (as vinyl acetate groups), which will bediscussed in further detail below.

Suitable poly(vinyl acetal) resins may include residues of any aldehydeand, in some embodiments, may include residues of at least one C₄ to C₈aldehyde. Examples of suitable C₄ to C₈ aldehydes can include, forexample, n-butyraldehyde, i-butyraldehyde (also referred to asiso-butyraldehyde), 2-methylvaleraldehyde, n-hexyl aldehyde,2-ethylhexyl aldehyde, n-octyl aldehyde, and combinations thereof. Oneor more of the poly(vinyl acetal) resins utilized in the layers andinterlayers described herein can include at least about 20, at leastabout 30, at least about 40, at least about 50, at least about 60, or atleast about 70 weight percent of residues of at least one C₄ to C₈aldehyde, based on the total weight of aldehyde residues of the resin.Alternatively, or in addition, the poly(vinyl acetal) resin may includenot more than about 99, not more than about 95, not more than about 90,not more than about 85, not more than about 80, not more than about 75,not more than about 70, or not more than about 65 weight percent of atleast one C₄ to C₈ aldehyde. The C₄ to C₈ aldehyde may be selected fromthe group listed above, or it can be selected from the group consistingof n-butyraldehyde, i-butyraldehyde, 2-ethylhexyl aldehyde, andcombinations thereof.

In various embodiments, the poly(vinyl acetal) resin may be a poly(vinylbutyral) (PVB) resin that primarily comprises residues ofn-butyraldehyde, and may, for example, include not more than about 30,not more than about 20, not more than about 10, not more than about 5,not more than about 2, or not more than 1 weight percent of residues ofan aldehyde other than n-butyraldehyde. Typically, the aldehyde residuesother than n-butyraldehyde present in poly(vinyl butyral) resins mayinclude iso-butyraldehyde, 2-ethylhexyl aldehyde, and combinationsthereof. When the poly(vinyl acetal) resin comprises a poly(vinylbutyral) resin, the weight average molecular weight of the resin can beat least about 30,000, at least about 40,000, at least about 50,000, atleast about 65,000, at least about 75,000, at least about 85,000, atleast about 100,000, or at least about 125,000 Daltons and/or not morethan about 500,000, not more than about 450,000, not more than about300,000, not more than about 350,000, not more than about 300,000, notmore than about 250,000, not more than about 200,000, not more thanabout 170,000, not more than about 160,000, not more than about 155,000,not more than about 150,000, not more than about 140,000, or not morethan about 135,000 Daltons, measured by size exclusion chromatographyusing low angle laser light scattering (SEC/LALLS) method of Cotts andOuano in tetrahydrofuran.

In general, poly(vinyl acetal) resins can be produced by hydrolyzing apoly(vinyl acetate) to poly(vinyl alcohol), and then acetalizing thepoly(vinyl alcohol) with one or more of the above aldehydes to form apoly(vinyl acetal) resin. In the process of hydrolyzing the poly(vinylacetate), not all the acetate groups are converted to hydroxyl groups,and, as a result, residual acetate groups remain on the resin.Similarly, in the process of acetalizing the poly(vinyl alcohol), notall of the hydroxyl groups are converted to acetal groups, which alsoleaves residual hydroxyl groups on the resin. As a result, mostpoly(vinyl acetal) resins include both residual hydroxyl groups (asvinyl hydroxyl groups) and residual acetate groups (as vinyl acetategroups) as part of the polymer chain. As used herein, the terms“residual hydroxyl content” and “residual acetate content” refer to theamount of hydroxyl and acetate groups, respectively, that remain on aresin after processing is complete. Both the residual hydroxyl contentand the residual acetate content are expressed in weight percent, basedon the weight of the polymer resin, and are measured according to ASTMD-1396.

The poly(vinyl acetal) resins utilized in one or more polymer layers asdescribed herein may have a residual hydroxyl content of at least about8, at least about 8.5, at least about 9, at least about 10, at leastabout 11, at least about 12, at least about 13, at least about 14, atleast about 15, at least about 16, at least about 17, at least about 18,at least about 18.5, at least about 19, at least about 20, at leastabout 21, at least about 22, at least about 23, at least about 24, atleast about 25, at least about 26, at least about 27, at least about 28,at least about 29, at least about 30, at least about 31, at least about32, or at least about 33 weight percent or more. Additionally, thepoly(vinyl acetal) resin or resins utilized in polymer layers of thepresent invention may have a residual hydroxyl content of not more thanabout 45, not more than about 43, not more than about 40, not more thanabout 37, not more than about 35, not more than about 34, not more thanabout 33, not more than about 32, not more than about 31, not more thanabout 30, not more than about 29, not more than about 28, not more thanabout 27, not more than about 26, not more than about 25, not more thanabout 24, not more than about 23, not more than about 22, not more thanabout 21, not more than about 20, not more than about 19, not more thanabout 18.5, not more than about 18, not more than about 17, not morethan about 16, not more than about 15, not more than about 14, not morethan about 13, not more than about 12, not more than about 11, or notmore than about 10 weight percent. Other residual hydroxyl contents maybe used or selected as desired depending on the application and desiredproperties.

When a polymer layer or interlayer includes more than one type ofpoly(vinyl acetal) resin, each of the poly(vinyl acetal) resins may havesubstantially the same residual hydroxyl contents, or one or more of thepoly(vinyl acetal) resins may have a residual hydroxyl contentsubstantially different from one or more other poly(vinyl acetal)resins. Various embodiments of several interlayers that include morethan one poly(vinyl acetal) resin are discussed in further detail below.

One or more poly(vinyl acetal) resins used in interlayers according tothe present invention may have a residual acetate content of not morethan about 20, not more than about 18, not more than about 15, not morethan about 12, not more than about 10, not more than about 8, not morethan about 6, not more than about 4, not more than about 3, or not morethan about 2 weight percent. Alternatively, or in addition, at least onepoly(vinyl acetal) resin used in a polymer layer or interlayer asdescribed herein can have a residual acetate content of at least about3, at least about 4, at least about 5, at least about 6, at least about7, at least about 8, at least about 9, at least about 10, at least about12, or at least about 14 weight percent or more. When a polymer layer orinterlayer includes two or more poly(vinyl acetal) resins, the resinsmay have substantially the same residual acetate content, or one or moreresins may have a residual acetate content different from the residualacetate content of one or more other poly(vinyl acetal) resins.

One or more polymer layers may also include at least one plasticizer.When present, the plasticizer content of one or more polymer layers canbe at least about 2, at least about 5, at least about 6, at least about8, at least about 10, at least about 15, at least about 20, at leastabout 25, at least about 30, at least about 35, at least about 40, atleast about 45, at least about 50, at least about 55, at least about 60,at least about 65, at least about 70, at least about 75, or at leastabout 80 parts per hundred resin (phr) and/or not more than about 120,not more than about 110, not more than about 105, not more than about100, not more than about 95, not more than about 90, not more than about85, not more than about 75, not more than about 70, not more than about65, not more than about 60, not more than about 55, not more than about50, not more than about 45, not more than about 40, or not more thanabout 35 phr. In some embodiments, one or more polymer layers can have aplasticizer content of less than 35, not more than about 32, not morethan about 30, not more than about 27, not more than about 26, not morethan about 25, not more than about 24, not more than about 23, not morethan about 22, not more than about 21, not more than about 20, not morethan about 19, not more than about 18, not more than about 17, not morethan about 16, not more than about 15, not more than about 14, not morethan about 13, not more than about 12, not more than about 11, or notmore than about 10 phr.

As used herein, the term “parts per hundred resin” or “phr” refers tothe amount of plasticizer present per one hundred parts of resin, on aweight basis. For example, if 30 grams of plasticizer were added to 100grams of a resin, the plasticizer content would be 30 phr. If thepolymer layer includes two or more resins, the weight of plasticizer iscompared to the combined amount of all resins present to determine theparts per hundred resin. Further, when the plasticizer content of alayer or interlayer is provided herein, it is provided with reference tothe amount of plasticizer in the mix or melt that was used to producethe layer or interlayer, unless otherwise specified.

For layers of unknown plasticizer content, the plasticizer content canbe determined via a wet chemical method in which an appropriate solvent,or mixture of solvents, is used to extract the plasticizer from thepolymer layer or interlayer. Prior to extracting the plasticizer, theweight of the sample layer is measured and compared with the weight ofthe layer from which the plasticizer has been removed after extraction.Based on this difference, the weight of plasticizer can be determinedand the plasticizer content, in phr, calculated. For multiple layerinterlayers, the polymer layers can be physically separated from oneanother and individually analyzed according to the above procedure.

Although not wishing to be bound by theory, it is understood that, for agiven type of plasticizer, the compatibility of the plasticizer in thepoly(vinyl acetal) resin may be correlated to the residual hydroxylcontent of the resin. More particularly, poly(vinyl acetal) resinshaving higher residual hydroxyl contents may generally have a reducedplasticizer compatibility or capacity, while poly(vinyl acetal) resinswith a lower residual hydroxyl content may exhibit an increasedplasticizer compatibility or capacity. Generally, this correlationbetween the residual hydroxyl content of a polymer and its plasticizercompatibility/capacity can be manipulated in order to facilitateaddition of the proper amount of plasticizer to the polymer resin and tostably maintain differences in plasticizer content between multiplelayers within an interlayer.

Any suitable plasticizer can be used in the polymer layers describedherein. The plasticizer may have a hydrocarbon segment of at least about6 and/or not more than about 30, not more than about 25, not more thanabout 20, not more than about 15, not more than about 12, or not morethan about 10 carbon atoms. Examples of plasticizers include esters of apolybasic acid or a polyhydric alcohol, among others. More specificexamples of suitable plasticizers include, but are not limited to,triethylene glycol di-(2-ethylhexanoate) (“3GEH”), triethylene glycoldi-(2-ethylbutyrate), tetraethylene glycol di-(2-ethylhexanoate)(“4GEH”), triethylene glycol diheptanoate, tetraethylene glycoldiheptanoate, dihexyl adipate, dioctyl adipate, hexyl cyclohexyladipate,diisononyl adipate, heptylnonyl adipate, dibutyl sebacate, butylricinoleate, castor oil, dibutoxy ethyl phthalate, diethyl phthalate,dibutyl phthalate, trioctyl phosphate, triethyl glycol ester of coconutoil fatty acids, phenyl ethers of polyethylene oxide rosin derivatives,oil modified sebacic alkyd resins, tricresyl phosphate, and mixturesthereof. In some embodiments, the plasticizer may comprise, or consistof, 3GEH. Other examples of plasticizers can include phosphate esters,epoxidized oil, solid state plasticizers, fire retardant plasticizers,and combinations thereof.

Additionally, one or more polymer layers of the present invention mayinclude at least one plasticizer having a refractive index greater thanabout 1.460, or greater than 1.470, or greater than 1.480. Examples ofsuch plasticizers can include, but are not limited to, esters of apolybasic acid or a polyhydric alcohol, polyadipates, epoxides,phthalates, terephthalates, benzoates, toluates, mellitates and otherspecialty plasticizers. Further examples include, but are not limitedto, dipropylene glycol dibenzoate, tripropylene glycol dibenzoate,polypropylene glycol dibenzoate, isodecyl benzoate, 2-ethylhexylbenzoate, diethylene glycol benzoate, propylene glycol dibenzoate,2,2,4-trimethyl-1,3-pentanediol dibenzoate,2,2,4-trimethyl-1,3-pentanediol benzoate isobutyrate, 1,3-butanedioldibenzoate, diethylene glycol di-o-toluate, triethylene glycoldi-o-toluate, dipropylene glycol di-o-toluate, 1,2-octyl dibenzoate,tri-2-ethylhexyl trimellitate, di-2-ethylhexyl terephthalate, bis-phenolA bis(2-ethylhexaonate), ethoxylated nonylphenol, and mixtures thereof.In some embodiments, the plasticizer can be selected from the groupconsisting of dipropylene glycol dibenzoates, tripropylene glycoldibenzoates, and combinations thereof.

Additionally, at least one of the polymer layers may also include othertypes of additives that can impart particular properties or features tothe polymer layer or interlayer. Such additives can include, but are notlimited to, adhesion control agents (“ACAs”), dyes, pigments,stabilizers such as ultraviolet stabilizers, antioxidants, anti-blockingagents, flame retardants, IR absorbers or blockers such as indium tinoxide, antimony tin oxide, lanthanum hexaboride (LaB₆) and cesiumtungsten oxide, processing aides, flow enhancing additives, lubricants,impact modifiers, nucleating agents, thermal stabilizers, UV absorbers,dispersants, surfactants, chelating agents, coupling agents, adhesives,primers, reinforcement additives, and fillers. Specific types andamounts of such additives may be selected based on the final propertiesor end use of a particular interlayer.

The polymer layers described herein may exhibit a wide range of glasstransition temperatures. In some embodiments, interlayers including twoor more polymers or polymer layers can exhibit two or more glasstransition temperatures. The glass transition temperature (T_(g)) of apolymeric material is the temperature that marks the transition of thematerial from a glass state to a rubbery state. The glass transitiontemperatures of the polymer layers can be determined by dynamicmechanical thermal analysis (DMTA) according to the following procedure.A polymer sheet is molded into a sample disc of 25 millimeters (mm) indiameter. The polymer sample disc is placed between two 25-mm diameterparallel plate test fixtures of a Rheometrics Dynamic Spectrometer II.The polymer sample disc is tested in shear mode at an oscillationfrequency of 1 Hertz as the temperature of the sample is increased from−20 to 70° C. at a rate of 2° C./minute. The position of the maximumvalue of tan delta (damping) plotted as dependent on temperature is usedto determine the glass transition temperature. Experience indicates thatthe method is reproducible to within +/−1° C.

Interlayers as described herein may include at least one polymer layerhaving a glass transition temperature of at least about −5, at leastabout −2, at least about −1, at least about 0, at least about 1, atleast about 2, at least about 5, at least about 10, at least about 15,at least about 20, at least about 25, at least about 27, at least about30, at least about 32, at least about 33, at least about 35, at leastabout 36, at least about 37, at least about 38, at least about 40, atleast about 41, at least about 42, at least about 43, at least about 44,at least about 45, at least about 46, at least about 47, at least about48, at least about 49, at least about 50, at least about 51, at leastabout 52, at least about 53, at least about 54, or at least about 55° C.or more. While there is no maximum glass transition temperature in someembodiments, in other embodiments, the polymer layer can have a glasstransition temperature of not more than about 80, not more than about78, not more than about 75, not more than about 70, not more than about65, not more than about 64, not more than about 63, not more than about62, not more than about 61, not more than about 60, not more than about59, not more than about 58, not more than about 57, not more than about56, not more than about 55, not more than about 54, not more than about53, not more than about 52, not more than about 51, not more than about50, not more than about 49, not more than about 48, not more than about47, not more than about 46, not more than about 45, not more than about44, not more than about 43, not more than about 42, not more than about41, not more than about 40, not more than about 39, not more than about38, not more than about 37, not more than about 36, not more than about35, not more than about 34, not more than about 33, not more than about32, not more than about 30, not more than about 25, not more than about20, not more than about 15, not more than about 10, not more than about5, not more than about 2, not more than about 1, not more than about 0,or not more than about −1° C. When a polymer layer or interlayerincludes two or more polymer layers, at least one of the layers may havea glass transition temperature different from one or more other polymerlayers within the interlayer. Other glass transition temperature(s) maybe selected depending on the desired properties and application. Variousembodiments of multiple layer interlayers will be discussed in furtherdetail shortly.

According to some embodiments of the present invention, the interlayermay be a single layer, or monolithic, interlayer. When the interlayer isa monolithic interlayer, the single polymer layer may include at leastone poly(vinyl acetal) resin and at least one plasticizer. Thepoly(vinyl acetal) resin may have properties that fall within one ormore of the ranges, and the plasticizer may be of the type and in theamounts described above. For example, in some embodiments, thepoly(vinyl acetal) resin can have a residual hydroxyl content of atleast about 19, at least about 20, at least about 21, at least about 22,at least about 23, at least about 24, at least about 25, at least about26, at least about 27, at least about 28, at least about 29, or at leastabout 30 weight percent and/or not more than about 45, not more thanabout 43, not more than about 40, not more than about 37, not more thanabout 35, not more than about 34, not more than about 33, or not morethan about 32 weight percent.

In some embodiments, the amount of plasticizer in the single polymerlayer interlayer can be not more than about 30, not more than about 27,not more than about 26, not more than about 25, not more than about 24,not more than about 23, not more than about 22, not more than about 21,not more than about 20, not more than about 19, not more than about 18,not more than about 17, not more than about 16, not more than about 15,not more than about 14, not more than about 13, not more than about 12,not more than about 11, or not more than about 10 phr. In someembodiments, the plasticizer content can be at least about 2, at leastabout 5, at least about 6, at least about 8, or at least about 10 phr,while, in other embodiments, the plasticizer content may be at or nearzero.

Additionally, the single polymer layer interlayer may have a glasstransition temperature greater than 43, at least about 44, at leastabout 45, greater than 46, at least about 47, at least about 48, atleast about 49, at least about 50, at least about 51, at least about 52,at least about 53, at least about 54, at least about 55, or at leastabout 56, at least about 60, at least about 65, at least about 70, atleast about 75, at least about 80, at least about 85, at least about 90,at least about 95, or at least about 100° C. or more. In someembodiments, at least two properties selected from the group consistingof residual hydroxyl content of the poly(vinyl acetal) resin,plasticizer content, and glass transition temperature for a singlepolymer layer may fall within the above ranges, while, in otherembodiments, the residual hydroxyl content of the poly(vinyl acetal)resin, the plasticizer content, and the glass transition temperature forthe single polymer layer may fall within one or more of the rangesdescribed herein.

Whether single or multiple layer, interlayers according to variousembodiments of the present invention may include at least two differentpolymers. When the layer or interlayer includes more than one polymer,each polymer may be present in an amount of at least about 0.5, at leastabout 1, at least about 2, at least about 5, at least about 10, at leastabout 15, at least about 20, at least about 30, at least about 40, or atleast about 45 weight percent, based on the combined weight of allpolymers present in the layer or interlayer. Additionally, one or moreof the polymers may be present in the interlayer in an amount of notmore than about 45, not more than about 40, not more than about 35, notmore than about 30, not more than about 25, not more than about 20, notmore than about 18, not more than about 15, not more than about 10, notmore than about 8, or not more than about 5 weight percent, based on thetotal weight of the polymer layer or interlayer, and together, thepolymers can make up at least about 10, at least about 20, at leastabout 30, at least about 40, at least about 50, at least about 60, atleast about 70, or at least about 80 weight percent of a layer orinterlayer, based on the combined weight of all components. According tosome embodiments, the total amount of components other than the polymersdescribed herein present in a layer or interlayer can be not more thanabout 20, not more than about 15, not more than about 10, not more thanabout 5, not more than about 2, or not more than about 1 weight percent,based on the combined weight of all components of the layer orinterlayer.

When present, the two or more different polymers may include at least afirst poly(vinyl acetal) resin and a second poly(vinyl acetal) resin.The first and second poly(vinyl acetal) resins may be present inadjacent layers of a multiple layer interlayer, or the first and secondpoly(vinyl acetal) resins may be physically mixed with one another so asto form a blended polymer layer or interlayer. As used herein, the terms“first,” “second,” “third,” and the like are used to describe variouselements, but such elements should not be unnecessarily limited by theseterms. These terms are only used to distinguish one element from anotherand do not necessarily imply a specific order or even a specificelement. For example, an element may be regarded as a “first” element inthe description and a “second” element in the claims without beinginconsistent. Consistency is maintained within the description and foreach independent claims, but such nomenclature is not necessarilyintended to be consistent therebetween.

When present, the first and second poly(vinyl acetal) resins can havedifferent compositions. For example, in some embodiments, the firstpoly(vinyl acetal) resin can have a residual hydroxyl content that is atleast about 2, at least about 3, at least about 4, at least about 5, atleast about 6, at least about 7, at least about 8, at least about 9, atleast about 10, at least about 12, at least about 13, at least about 14,at least about 15, at least about 16, at least about 17, at least about18, at least about 19, at least about 20, at least about 21, at leastabout 22, at least about 23, or at least about 24 weight percentdifferent than the residual hydroxyl content of the second poly(vinylacetal) resin. In other embodiments, the first poly(vinyl acetal) resincan have a residual hydroxyl content that is not more than about 2, notmore than about 1.5, not more than about 1, or not more than about 0.5weight percent different than the residual hydroxyl content of thesecond poly(vinyl acetal) resin.

Additionally, or in the alternative, the first poly(vinyl acetal) resincan have a residual acetate content that is at least about 2, at leastabout 3, at least about 4, at least about 5, at least about 7, at leastabout 8, at least about 9, at least about 10, at least about 12, atleast about 13, at least about 15, at least about 18, or at least about20 weight percent different than the residual acetate content of thesecond poly(vinyl acetal) resin. In other embodiments, the firstpoly(vinyl acetal) resin can have a residual acetate content that is notmore than about 2, not more than about 1.5, not more than about 1, ornot more than about 0.5 weight percent different than the residualacetate content of the second poly(vinyl acetal) resin.

As used herein, the term “weight percent different” or “the difference .. . is at least . . . weight percent” refers to a difference between twogiven percentages, calculated by finding the absolute value of themathematical difference between the two numbers. A value that is“different” from a given value can be higher or lower than the givenvalue. For example, a first poly(vinyl acetal) resin having a residualhydroxyl content that is “at least 2 weight percent different than” theresidual hydroxyl content of a second poly(vinyl acetal) resin may havea residual hydroxyl content that is at least 2 weight percent higher orat least 2 weight percent lower than the second residual hydroxylcontent. For example, if the residual hydroxyl content of the exemplarysecond poly(vinyl acetal) resin is 14 weight percent, the residualhydroxyl content of the exemplary first poly(vinyl acetal) resin can beat least 16 weight percent (e.g., at least 2 weight percent higher) ornot more than 12 weight percent (e.g., at least 2 weight percent lower).

As a result of having different compositions, the portions of the layeror interlayer formed from the first poly(vinyl acetal) resin and thesecond poly(vinyl acetal) resin may have different properties, due to,for example, differences in plasticizer content. As describedpreviously, when two poly(vinyl acetal) resins having different residualhydroxyl contents are blended with a plasticizer, the plasticizer maypartition between the different resins, such that a higher amount ofplasticizer is present in the portion of the layer or interlayer formedfrom the lower residual hydroxyl content resin and less plasticizer ispresent in the portion of the layer or interlayer formed from the higherresidual hydroxyl content resin. Ultimately, a state of equilibrium isachieved between the two resins. The correlation between the residualhydroxyl content of a poly(vinyl acetal) resin and plasticizercompatibility/capacity can facilitate addition of a proper amount ofplasticizer to the polymer resin. Such a correlation also helps tostably maintain the difference in plasticizer content between two ormore resins when the plasticizer would otherwise migrate between theresins.

Although not wishing to be bound by theory, it is assumed that thecompatibility of a given plasticizer with a poly(vinyl acetal) resin candepend, at least in part, on the composition of the polymer, and, inparticular, on its residual hydroxyl content. Overall, poly(vinylacetal) resins with higher residual hydroxyl contents tend to exhibit alower compatibility (or capacity) for a given plasticizer as compared tosimilar resins having a lower residual hydroxyl content. As a result,poly(vinyl acetal) resins with higher residual hydroxyl contents tend tobe less plasticized and exhibit higher stiffness than similar resinshaving lower residual hydroxyl contents. Conversely, poly(vinyl acetal)resins having lower residual hydroxyl contents may tend to, whenplasticized with a given plasticizer, incorporate higher amounts ofplasticizer, which may result in a softer polymer layer that exhibits alower glass transition temperature than a polymer layer including asimilar resin having a higher residual hydroxyl content. Depending onthe specific resin and plasticizer, these trends could be reversed.

When the first and second poly(vinyl acetal) resins have differentresidual hydroxyl contents, the portions of the layer or interlayerformed from each of the first and second poly(vinyl acetal) resins mayalso include different amounts of plasticizer. As a result, each ofthese portions may also exhibit different properties, such as, forexample, glass transition temperature. In some embodiments, thedifference in plasticizer content between portions of a layer orinterlayer formed from a first poly(vinyl acetal) resin and the portionsof a layer or interlayer formed from a second poly(vinyl acetal) resincan be at least about 2, at least about 3, at least about 5, at leastabout 8, at least about 10, at least about 12, or at least about 15 phror more, measured as described above. In other embodiments, thedifference in plasticizer content between portions of a layer orinterlayer formed from a first poly(vinyl acetal) resin and portions ofa layer or interlayer formed from a second poly(vinyl acetal) resin canbe at least about 18, at least about 20, at least about 25, at leastabout 30, at least about 35, at least about 40, at least about 45, atleast about 50, at least about 55, at least about 60, or at least about65 phr or more.

In addition, or in the alternative, the difference between theplasticizer content of the portion of the layer or interlayer formedfrom the first polymer and the portion of the layer or interlayer formedfrom the second polymer may be not more than about 40, not more thanabout 35, not more than about 30, not more than about 25, not more thanabout 20, not more than about 17, not more than about 15 or not morethan about 12 phr. The values for the plasticizer content of theportions of the layer or interlayer formed from the first and secondpoly(vinyl acetal) resins may fall within one or more of the rangesprovided above.

In some embodiments, the glass transition temperature of the portion ofthe layer or interlayer formed from the first poly(vinyl acetal) resincan be at least about 3, at least about 5, at least about 8, at leastabout 10, at least about 12, at least about 13, at least about 15, atleast about 18, at least about 20, at least about 22, at least about 25,at least about 27, at least about 30, at least about 35, at least about40, at least about 45, at least about 50, at least about 55, at leastabout 60, at least about 65, or at least about 70° C. different than theportion of the layer or interlayer formed from the second poly(vinylacetal) resin. The values for the glass transition temperatures of theportions of the layer or interlayer formed from the first and secondpoly(vinyl acetal) resins may fall within one or more of the rangesprovided above.

When present in a blended polymer layer or interlayer, the first andsecond poly(vinyl acetal) resins may be combined such that the secondpoly(vinyl acetal) resin is dispersed within the first poly(vinylacetal) resin to thereby form domains of the second poly(vinyl acetal)resin within a substantially continuous phase formed from the firstpoly(vinyl acetal) resin. Each of the resins may be present in an amountof at least about 0.5, at least about 1, at least about 2, at leastabout 5, at least about 10, at least about 15, at least about 20, atleast about 30, at least about 40, at least about 45, or at least about50 weight percent, based on the combined weight of all polymers presentin the layer or interlayer. According to some embodiments, thedifference between the residual hydroxyl content of the first poly(vinylacetal) resin and the residual hydroxyl content of the second poly(vinylacetal) resin can be at least about 5, at least about 6, at least about7, at least about 8, at least about 9, at least about 10, at least about11, at least about 12, or at least about 13, at least about 14, at leastabout 15, at least about 16, at least about 17, at least about 18, atleast about 19, at least about 20, at least about 21, at least about 22,at least about 23, or at least about 24 weight percent.

The blended layer can further include one or more additional polymers,such as, for example, a third poly(vinyl acetal) resin, dispersed withinthe first poly(vinyl acetal) resin, to thereby additionally form domainsof the third poly(vinyl acetal) resin within the continuous phase of thefirst poly(vinyl acetal) resin. One or more other polymers in additionto the third poly(vinyl acetal) resin may also be blended into the firstpoly(vinyl acetal) resin, thereby forming further domains of otherpolymer material within the continuous phase formed by the firstpoly(vinyl acetal) resin. Further, additional polymer layers thatinclude one or more additional polymers as described previously, mayalso be present in the interlayer, adjacent to and in contact with theblended polymer layer.

When the blended layer includes at least a first, a second, and a thirdpoly(vinyl acetal) resin, the second and third poly(vinyl acetal) resinsmay be dispersed within the first poly(vinyl acetal) resin to therebyform domains of the second and third poly(vinyl acetal) resins withinthe continuous phase of the first poly(vinyl acetal) resin. According tosome embodiments, at least one of the poly(vinyl acetal) resins can havean “intermediate” residual hydroxyl content that is lower than theresidual hydroxyl content of the resin having the highest residualhydroxyl content, and higher than the residual hydroxyl content of theresin having the lowest residual hydroxyl content.

In such embodiments, the difference between the highest and lowestresidual hydroxyl contents (i.e., the maximum residual hydroxyldifference) can be at least about 5, at least about 6, at least about 7,at least about 8, at least about 9, at least about 10, at least about11, at least about 12, or at least about 13 weight percent, while theindividual differences between the highest and intermediate residualhydroxyl contents and intermediate and lowest residual hydroxyl contentscan be not more than about 4, not more than about 3, not more than about2, not more than about 1 weight percent. In some embodiments, when theblended polymer layer includes at least 4, at least 5, at least 6, or atleast 7 poly(vinyl acetal) resins of different residual hydroxylcontents, none of the resins may have a residual hydroxyl content thatdiffers from the resin having the next largest and next smallest valuesfor residual hydroxyl content by more than 1 percent, more than 2percent, more than 3 percent, or more than 4 percent.

In some embodiments, use of one or more resins having an intermediateresidual hydroxyl content as described above may help minimize hazewhile enhancing other properties of the interlayer, especially as themaximum residual hydroxyl difference exceeds 5 weight percent. In someembodiments, blended polymer layers may also include at least one highrefractive index plasticizer having, for example, a refractive index ofat least about 1.460, at least about 1.465, at least about 1.470, atleast about 1.475, at least about 1.480, at least about 1.485, at leastabout 1.490, at least about 1.495, at least about 1.500, or at leastabout 1.510, measured according to ASTM D542 at a wavelength of 589 nmand 25° C. Examples of suitable high refractive index plasticizers areprovided above, and at least one can be used in any amount required toachieve desirable optical and other properties in the final layer orinterlayer.

When the interlayer includes first and second poly(vinyl acetal) resinsthat are present in two or more layers of a multilayer interlayer, oneof the polymer layers can include the first poly(vinyl acetal) resin andanother polymer layer can include the second poly(vinyl acetal) resin.Additional polymer layers that include one or more additional polymers,including other poly(vinyl acetal) resins, may also be present in theinterlayer, adjacent to and in contact with at least one of the firstand second polymer layers. When other polymers are present in additionalpolymer layers of an interlayer, the other polymers can be of the typesand in the amounts as described previously.

In some embodiments, the interlayers described herein can include atleast a first outer polymer layer and a second outer polymer layer. Asused herein, the term “outer” refers to the outermost layer or layers ofan interlayer. Typically, the outer polymer layers are configured to bein contact with a substrate when the interlayer is laminated to thesubstrate, or to one of a pair of substrates when the interlayer is usedto form a multiple layer panel. In some embodiments, each of the firstand second outer polymer layers can include respective first and secondpoly(vinyl acetal) resins and an optional plasticizer, and the resinsmay have residual hydroxyl contents and residual acetate contents withinone or more of the ranges provided above. Similarly, each of the firstand second polymer layers can include at least one plasticizer of a typeand in the amounts described above, so that the layers may also have aglass transition temperature as previously described.

According to some embodiments, the first and second outer polymer layersmay be adjacent to and in contact with one another, such that the firstand second outer polymer layers are the only two layers of theinterlayer. In other embodiments, at least 1, at least 2, at least 3, atleast 4, or at least 5 or more polymer layers may be disposed betweenand in contact with at least one of the first and second outer polymerlayers. These additional layers, when present, may have compositionssimilar to, or different than, each of the first and second polymerlayers and may include one or more of the polymers described above. Theadditional layers may also be formed of other materials, such as apolymer film formed from polyethylene terephthalate (PET), and thepolymer film may include various metallic, metal oxide, or othernon-metallic materials or layers and may be coated or otherwisesurface-treated. In some embodiments, one or more of the additionallayers may comprise functional layers such including, for example, IRreducing layers, holographic layers, photochromic layers, electrochromiclayers, antilacerative layers, heat strips, antennas, solar radiationblocking layers, decorative layers, and the like.

In some embodiments, the interlayer can include at least a first polymerlayer, a second polymer layer, and a third polymer layer, wherein thesecond polymer layer is disposed between and in contact with each of thefirst and third polymer layers. Each of the respective first, second,and third polymer layers can include at least one poly(vinyl acetal)resin and an optional plasticizer of the types and in the amountsdescribed in detail previously. According to some embodiments, thesecond, inner polymer layer can include a resin having a residualhydroxyl content higher than the residual hydroxyl contents of thepoly(vinyl acetal) resins in each of the first and third polymer layers.Consequently, as the plasticizer partitions between the layers, thesecond inner layer may have a glass transition temperature higher thanthe glass transition temperatures of each of the first and third outerpolymer layers. Although not wishing to be bound by theory, it isunderstood that this type of configuration, wherein relatively “soft”(i.e., lower glass transition temperature) outer polymer layers aresandwiching a “stiff” (i.e., relatively high glass transitiontemperature) inner layer, may facilitate both enhanced rigidity andimpact resistance in multiple layer panels formed from the interlayer.

In some embodiments, the first and third outer polymer layers can havethe same or similar compositions and/or properties. For example, in someembodiments, the poly(vinyl acetal) resin in the first polymer layer canhave a residual hydroxyl content within about 2, within about 1, orwithin about 0.5 weight percent of the residual hydroxyl content of thepoly(vinyl acetal) resin in the third polymer layer. Similarly, thepoly(vinyl acetal) resins in the first and third layer can have residualacetate contents within about 2, within about 1, or within about 0.5weight percent of one another. Additionally, the first and third outerpolymer layers may have similar plasticizer contents and/or may exhibitsimilar glass transition temperatures. For example, the plasticizercontent of the first polymer layer can be less than 2, not more thanabout 1, or not more than about 0.5 phr different than the plasticizercontent of the third polymer layer, and/or the first and third polymerlayers can have glass transition temperatures that differ by less than2, not more than about 1, or not more than about 0.5° C.

In other embodiments, the first and third outer polymer layers can havedifferent compositions and/or properties. For example, in someembodiments, the residual hydroxyl and/or residual acetate content ofthe poly(vinyl acetal) resin in the first polymer layer can be at leastabout 2, at least about 3, at least about 5, at least about 8, or atleast about 10 weight percent and/or not more than about 20, not morethan about 18, not more than about 15, not more than about 12, not morethan about 10 weight percent different than the residual hydroxyl and/orresidual acetate content of the poly(vinyl acetal) resin in the thirdpolymer layer. In some embodiments, the plasticizer content of the firstand third polymer layers may also differ by at least about 2, at leastabout 3, at least about 5, or at least about 8 phr and/or not more thanabout 20, not more than about 15, not more than about 12, or not morethan about 10 phr. Consequently, the glass transition temperature of thefirst polymer layer may be at least about 2, at least about 3, at leastabout 5, at least about 8, or at least about 10° C. and/or not more thanabout 20, not more than about 15, not more than about 12, or not morethan about 10° C. different than the glass transition temperature of thethird polymer layer. In some embodiments, interlayers that include twoouter polymer layers having different compositions and/or properties maybe useful for panels exposed to widely different conditions on oppositesides of the laminate, such as, for example, architectural panels usedin extreme climates.

According to some embodiments of the present invention, at least onepolymer layer of a multiple layer interlayer may not include apoly(vinyl acetal) resin. Such layers can, for example, include lessthan about 2, less than about 1.5, less than about 1, less than about0.5, or less than about 0.10 weight percent of poly(vinyl acetal)resins, based on the total weight of the polymer layer. Polymer layersthat do not include a poly(vinyl acetal) resin may, instead, include atleast one of the other polymer resins discussed in detail previously. Insome embodiments, at least one of the layers of a multiple layerinterlayer may include a polymer selected from the group consisting ofpolyurethanes (PU), poly(ethylene-co-vinyl) acetates (EVA), poly(vinylchlorides) (PVC), cellulose esters, acid copolymers such asethylene/carboxylic acid copolymers and ionomers and combinationsthereof, although other polymers are also possible. The polymer otherthan a poly(vinyl acetal) resin may exhibit different properties than apolymer layer comprising a poly(vinyl acetal) resin. For example, insome embodiments, at least a portion of the polymer layer includinganother polymer resin may be cross-linked, whereas polymer layersincluding a poly(vinyl acetal) resin generally would not be.

In some cases, such interlayers may further include one or more polymerlayers that include a poly(vinyl acetal) resin, as discussed above,adjacent to and in contact with at least one layer that does not includea poly(vinyl acetal) resin. For example, in some embodiments, theinterlayer may include at least one outer polymer layer comprising apoly(vinyl acetal) resin and at least one inner layer comprising athermoplastic polymer other than a poly(vinyl acetal) resin. Inembodiments, the thermoplastic polymer other than the poly(vinyl acetal)resin may have a glass transition temperature that is greater than theglass transition temperature of the poly(vinyl acetal) resin in theouter layer(s), such as greater than about 43° C., and a modulus (G′)that is higher than the modulus of the outer or skin layer(s), such asgreater than about 1 MPa at 50° C. In embodiments, the outer layer mayhave a glass transition temperature of less than about 43° C. Accordingto such embodiments, the poly(vinyl acetal) resin may have a residualhydroxyl content of not more than about 23, not more than about 22, notmore than about 21, not more than about 20, not more than about 19, notmore than about 18, not more than about 17, not more than about 16.5,not more than about 16, not more than about 15.5, not more than about15, not more than about 14.5, not more than about 14, not more thanabout 13.5, not more than about 13, not more than about 12.5, not morethan about 12, not more than about 11.5, not more than about 11, notmore than about 10.5, not more than about 10, or not more than about 9.5weight percent, and the glass transition temperature of the outerpolymer layer can be not more than about 40, not more than about 35, notmore than about 33, not more than about 32, not more than about 30, notmore than about 27, not more than about 25, not more than about 20, notmore than about 15, not more than about 10, not more than about 5, notmore than about 2, not more than about 1, not more than about 0, or notmore than about −2° C.

In other embodiments, the interlayer may include at least one innerpolymer layer comprising a poly(vinyl acetal) resin and at least oneouter polymer layer comprising a thermoplastic polymer other than apoly(vinyl acetal) resin. In embodiments, the thermoplastic polymerother than the poly(vinyl acetal) resin may have a glass transitiontemperature that is less than the glass transition temperature of thepoly(vinyl acetal) resin in the core layer, such as less than about 40°C., and a modulus (G′) that is less than the modulus of the core layer,such as less than about 1 MPa at 50° C. In embodiments, the core layermay have a glass transition temperature of greater than about 43° C. Inaccordance with these embodiments, the poly(vinyl acetal) resin can havea residual hydroxyl content of at least about 10, at least about 11, atleast about 12, at least about 13, at least about 14, at least about 15,at least about 16, at least about 17, at least about 18, at least about18.5, at least about 19, at least about 19.5, at least about 20, atleast about 20.5, at least about 21, at least about 21.5, at least about22, at least about 22.5, at least about 23, at least about 23.5, atleast about 24, at least about 24.5, at least about 25, at least about25.5 weight percent, or higher.

The plasticizer content of the inner poly(vinyl acetal) resin-containingpolymer layer can be less than 35, not more than about 32, not more thanabout 30, not more than about 27, not more than about 26, not more thanabout 25, not more than about 24, not more than about 23, not more thanabout 22, not more than about 21, not more than about 20, not more thanabout 19, not more than about 18, not more than about 17, not more thanabout 16, not more than about 15, not more than about 14, not more thanabout 13, not more than about 12, not more than about 11, or not morethan about 10 phr, and/or the glass transition temperature can be atleast about 35, at least about 36, at least about 37, at least about 38,at least about 40, at least about 41, at least about 42, at least about43, at least about 44, at least about 45, at least about 46, at leastabout 47, at least about 48, at least about 49, at least about 50, atleast about 51, at least about 52, at least about 53, at least about 54,or at least about 55° C.

According to embodiments wherein the interlayer includes one polymerlayer comprising a poly(vinyl acetal) resin and another polymer layercomprising a resin or polymer other than a poly(vinyl acetal) resin,each layer may have different properties. For example, in someembodiments, the polymer layers may have glass transition temperaturesthat differ from one another by at least about 3, at least about 5, atleast about 7, at least about 10, at least about 12, at least about 15,at least about 20, at least about 25, at least about 30, at least about35, at least about 40, at least about 45, at least about 50, at leastabout 55, at least about 60, at least about 65, at least about 70, atleast about 75, at least about 80, at least about 85, at least about 90,at least about 95, at least about 100, at least about 105, at leastabout 110, at least about 115, or at least about 120° C. The polymerlayer including the resin other than a poly(vinyl acetal) resin can havea glass transition temperature higher or lower than the polymer layerincluding the poly(vinyl acetal) resin.

According to some embodiments, the glass transition temperature of thepolymer layer that does not include a poly(vinyl acetal) resin can benot more than about 20, not more than about 15, not more than about 10,not more than about 5, not more than about 0, not more than about −5,not more than about −10, not more than about −15, not more than about−20, not more than about −25, not more than about −30, not more thanabout −35, or not more than about −40° C. Alternatively, or in addition,the glass transition temperature of the polymer layer that does notinclude a poly(vinyl acetal) resin can be at least about −50, at leastabout −45, at least about −40, at least about −35, at least about −30,at least about −25, at least about −20, at least about −15, at leastabout −10, at least about −5, at least about 0, or at least about 5° C.,or it can be in the range of from −50 to 0° C., from −45 to −10° C., or−40 to −20° C. Other glass transition temperatures are also possibleand, in some embodiments, the glass transition temperature of thepolymer layer including the poly(vinyl acetal) resin and/or the polymerlayer that does not include a poly(vinyl acetal) resin can be within oneor more of the ranges described above.

Interlayers according to various embodiments of the present inventionmay exhibit enhanced properties as compared to conventional interlayers.For example, in contrast to comparative interlayers used forarchitectural applications, interlayers as described herein may exhibitboth high rigidity and good impact performance, while still retainingsuitable optical characteristics. As a result, interlayers as describedherein may suitably be utilized in many structural and load-bearingapplications, subject to various pressures, temperature changes, andimpacts, while maintaining both suitable performance and aesthetic valueand properties.

Interlayers as described herein may exhibit an enhanced rigidity.Rigidity of a polymer layer or interlayer may be characterized by itsshear storage modulus (G′), measured at 50° C. according to ASTMD4065-12. In some embodiments, a polymer layer or interlayer asdescribed herein may have a shear storage modulus (G′) at 50° C. of atleast about 2, at least about 3, at least about 3.5, at least about 4,at least about 4.5, at least about 5, at least about 5.5, at least about6, at least about 6.5, or at least about 7 MPa. There is no particularupper limit, although practically, the layer or interlayer may exhibit ashear storage modulus as high as 7.5 MPa or even as high as 8 MPa ormore at 50° C.

The rigidity of the interlayer may also be characterized according toits three-point bending stiffness. The three-point bending stiffness, asdescribed herein, is measured for an interlayer having a thickness of 30mils when the interlayer is laminated between two sheets of 2.3-mm thickclear glass, according to ASTM D790 at room temperature. In someembodiments, the interlayer can have a three-point bending stiffness ofat least about 100, at least about 105, at least about 110, at leastabout 115, at least about 120, at least about 125, at least about 130,at least about 135, at least about 140, at least about 145, at leastabout 150, at least about 155, at least about 160, at least about 170,at least about 180, at least about 190, at least about 200, at leastabout 210, at least about 220, at least about 230, at least about 240,at least about 250, at least about 260, at least about 270, at leastabout 280, at least about 290, or at least about 300 N/mm.

In addition to enhanced rigidity, interlayers according to embodimentsof the present invention can exhibit desirable impact resistance, ascharacterized by the mean break height of the interlayer, when having athickness of between 30 and 60 mils and when laminated between twosheets of 2.3-mm thick clear glass, measured according to ANSI/SAEZ26.1-1996 at a temperature of about 70° F. (about 21° C.). In someembodiments, the interlayers as described herein can have a mean breakheight, measured as described above, of at least about 13, at leastabout 13.5, at least about 14, at least about 14.5, at least about 15,at least about 15.5, at least about 16, at least about 16.5, at leastabout 17, at least about 17.5, at least about 18, at least about 18.5,at least about 19, at least about 19.5, at least about 20, at leastabout 20.5, at least about 21, at least about 21.5, at least about 22,at least about 22.5, at least about 23, at least about 23.5, at leastabout 24, at least about 24.5, or at least about 25 feet, at least about25.5, at least about 26, at least about 26.5, at least about 27, atleast about 27.5, at least about 28, or at least about 28.5 feet ormore. Mean break height can also be measured at other thicknesses. Inembodiments, the higher the mean break height, the better.

The values for mean break height provided herein are obtained using aninterlayer having a known thickness (as indicated), such as 30 mils, 45mils, or other thickness, laminated between two 2.3-mm thick sheets ofglass. The specification of values for these parameters is not intendedto, in any way, limit the thickness of the interlayers described hereinor the configuration of multiple layer panels according to embodimentsof the present invention. Rather, specification of values for theseparameters is intended to provide a definite test for determining theimpact resistance, measured as mean break height, exhibited by aninterlayer, and the test is measured at a known thickness and ifnecessary, normalized to a constant thickness (such as 30 mils or 45mils) so that different interlayers can be compared at the sameinterlayer thickness.

Interlayers of the present invention may be used to form panels thatexhibit a mean break height greater than the mean break height ofsimilar panels formed from a comparative interlayer. As used herein, theterm “comparative interlayer” refers to a monolithic interlayer formedfrom a poly(vinyl butyral) resin having a residual hydroxyl content of18.7 weight percent and a residual acetate content of less than 2percent plasticized with 20 phr of 3GEH plasticizer. In someembodiments, a single or multiple layer interlayer as described hereinmay exhibit a mean break height that it at least about 5, at least about10, at least about 15, at least about 20, at least about 25, at leastabout 30, at least about 35, at least about 40, at least about 45, atleast about 50, at least about 55, at least about 60, at least about 65,at least about 70, at least about 75, at least about 80, at least about85, or at least about 90 percent higher than the mean break height of acomparative interlayer having the same thickness.

Additionally, interlayers of the present invention have the capabilityof maintaining acceptable levels of creep resistance, when laminatedbetween two glass sheets to form a multiple layer panel. For example,interlayers of the present invention may exhibit a creep of not morethan about 1 mm, not more than about 0.9 mm, not more than about 0.8 mm,not more than about 0.7 mm, not more than about 0.6 mm, not more thanabout 0.5 mm, or not more than about 0.4 mm, when measured at atemperature of 100° C. for 1000 hours, according to the followingprocedure. A 6-inch by 6-inch interlayer to be tested is laminatedbetween two sheets of 2.3-mm thick clear glass, one having dimensions of6 inches by 6 inches and the other having dimensions of 6 inches by 7inches. The resulting glass panel is hung by the exposed 1-inch sectionof glass in an oven set at a temperature of 100° C. The specimen isremoved from the oven at predetermined intervals of 100 hours, 250hours, 500 hours, and 1000 hours. At each interval, the panel isanalyzed to determine how far (in mm) the smaller (6-inch by 6-inch)sheet of glass has moved from its original position relative to thelarger (6-inch by 7-inch) sheet of glass.

Pummel adhesion is another parameter that may be used to describe theinterlayers disclosed herein. The Pummel Adhesion Test measures theadhesion level of glass to the interlayer in a laminate construction.The interlayer to glass adhesion has a large effect on the impactresistance and long term stability of glass-interlayer structures. Inthis test, the laminates are cooled to 0° F. (−18° C.) and manuallypummeled with a 1 lb. (0.45 kg) hammer on a steel plate at a 45° angle.The samples are then allowed to come to room temperature and all brokenglass unadhered to the interlayer is then removed. The amount of glassleft adhered to the interlayer is visually compared with a set ofstandards. The standards correspond to a scale in which varying degreesof glass remained adhered to the interlayer. For example, at a pummelstandard of zero, essentially no glass is left adhered to theinterlayer. On the other hand, at a pummel standard of ten, essentially100 percent of the glass remains adhered to the interlayer. Pummelvalues are grouped and averaged for like specimens. Reported valuesstate the average pummel value for the group and the maximum range ofthe pummel adhesion rating for individual surfaces. The interlayersdescribed herein may have a pummel adhesion rating of 2 or greater, or 9or less, or from about 2 to about 9.

In addition to enhanced rigidity and impact performance, interlayersaccording to embodiments of the present invention also exhibit suitableoptical properties, which may vary depending on the ultimate end use.Clarity is one parameter used to describe the optical performance of theinterlayers described herein and may be determined by measuring hazevalue or percent. Haze value represents the quantification of lightscattered by a sample in contrast to the incident light. The test fordetermining haze value is performed with a hazemeter, such as a ModelD25 Hazemeter commercially available from Hunter Associates (Reston,Va.), on a polymer sample which has been laminated between two sheets ofclear glass, each having a thickness of 2.3 mm.

When the interlayer is used in a multiple layer panel for which a highlevel of optical clarity is desired, such as, for example, in clearwindows or windshields, the interlayer may be transparent or nearlytransparent. In some embodiments, interlayers of the present inventionmay have a haze value of less than about 3, less than about 2, less thanabout 1 percent, as measured in accordance with ASTM D1003-61(reapproved 1977)—Procedure B using Illuminant C, at an observer angleof 2 degrees. In other embodiments, when haze is less important, theinterlayer may have a higher haze value, such as, for example, at leastabout 25, at least about 30, or at least about 40 percent.

Another parameter used to determine the optical performance is percentvisual transmittance (% T_(vis)), which is measured on the HunterLabUltraScan XE, commercially available from Hunter Associates (Reston,Va.). The values may be obtained by analyzing a polymer sample which hasbeen laminated between two sheets of clear glass, each having athickness of 2.3 mm (commercially available from Pittsburgh Glass Worksof Pennsylvania). In some embodiments, when clear multiple layer panelsare desired, the interlayers of the present invention can have a percentvisual transmittance of at least about 80, at least about 81, at leastabout 82, at least about 83, at least about 84, at least about 85, atleast about 85.5, at least about 86, at least about 86.5, at least about87, at least about 87.5, or at least about 88, at least about 88.5percent or higher.

In embodiments when the transparency and/or haze of the interlayer isnot as important, the interlayer, or panel formed therefrom, may betranslucent, at least partially opaque, or totally opaque. Examples ofapplications for such panels include privacy glass or other similar enduses. According to some embodiments, such an interlayer may have, forexample, a haze value greater than about 30 percent. Alternatively, orin addition, the interlayer may have a visual transmittance of leastabout 2 percent, at least about 5 percent, at least about 10 percentand/or not more than about 40 percent, not more than about 35 percent,or not more than about 30 percent. Additionally, in some embodiments,the interlayers as described herein may have a reflectance (% R) greaterthan 5 percent, at least about 10 percent, or at least about 15 percentand/or not more than about 50, not more than about 45, or not more thanabout 40 percent, measured according to ASTM E-1164. Other values ofreflectance, transmittance, and haze may also be possible, depending onthe particular end use. Further, the levels of reflectance,transmittance, and haze may be controlled according to any suitablemethod including, for example, inclusion of additives, colorants, dyes,and other similar components.

Alternatively, or in addition, the layers, and interlayers as describedherein may have a mottle value of not more than 4, not more than 3, notmore than 2, or not more than about 1. Mottle is another measure ofoptical quality, which is detected as a texture or graininess. Mottle isa visual defect that is visible if the level of texture or graininess istoo high or too severe, thereby causing objectionable visual appearance.Mottle is assessed and categorized by a side-by-side qualitativecomparison of shadowgraph projections for a test laminate with a set ofstandard laminate shadowgraphs that represent a series, or scale, ofmottle values ranging from 1 to 4, with 1 representing a standard of lowmottle (i.e., a low number of disruptions) and 4 representing a standardof high mottle (i.e., a high number of disruptions). High mottle isgenerally considered objectionable, particularly in automotive andarchitectural applications. Optionally, a model laminate having a singlelayer interlayer with zero mottle (no mottle) is used to facilitate theevaluation in a test laminate that has a mottle rating lower than thescale of the standard set, such as lower than a rating of 1. A testlaminate that shows a shadowgraph projection similar to that of azero-mottle laminate is assessed to have a mottle rating of zero.

When the interlayer includes two or more resins, including, for example,two or more poly(vinyl acetal) resins, the refractive index (RI) of eachof the resins can be matched to prevent haze or other optical defectsfrom appearing in the resulting interlayer. Also, when the interlayerincludes two or more layers, including, for example, two or morepoly(vinyl acetal) layers, the refractive index (RI) of each of thelayers can be matched to prevent haze or other optical defects fromappearing in the resulting interlayer. In some embodiments, the polymerresins may be selected such that the maximum difference between theindividual refractive indices of the polymers is less than 0.010 units.For example, if an interlayer included three polymer resins, thedifference between the refractive index of the first resin and therefractive index of the second resin, the difference between therefractive index of the second resin and the refractive index of thethird resin, and the difference between the refractive index of thefirst resin and the refractive index of the third resin would each beless than 0.010. In some embodiments, one or more RI balancing agentsmay be included in at least one polymer layer of the interlayer to helpfacilitate RI matching of the various polymers and/or the variouslayers. In some embodiments, the RI balancing agent can include at leastone of the high refractive index plasticizers listed above, while, inother embodiments, the RI balancing agent can be another component, suchas, for example a solid additive selected from the group consisting ofpolyadipates, polystyrene having a molecular weight of less than 2500,epoxides, phthalic acid esters, benzoic acid esters, and combinationsthereof.

The interlayers of the present invention can be formed according to anysuitable method. Exemplary methods can include, but are not limited to,solution casting, compression molding, injection molding, meltextrusion, melt blowing, and combinations thereof. Multilayerinterlayers including two or more polymer layers may also be producedaccording to any suitable method such as, for example, co-extrusion,blown film, melt blowing, dip coating, solution coating, blade, paddle,air-knife, printing, powder coating, spray coating, lamination, andcombinations thereof.

According to various embodiments of the present invention, the layers orinterlayers may be formed by extrusion or co-extrusion. In an extrusionprocess, one or more thermoplastic resin(s), plasticizer(s), and,optionally, one or more additives as described previously, can bepre-mixed and fed into an extrusion device. The extrusion device isconfigured to impart a particular profile shape to the thermoplasticcomposition in order to create an extruded sheet. The extruded sheet,which is at an elevated temperature and highly viscous throughout, canthen be cooled to form a polymeric sheet. Once the sheet has been cooledand set, it may be cut and rolled for subsequent storage,transportation, and/or use as an interlayer.

Co-extrusion is a process by which multiple layers of polymer materialare extruded simultaneously. Generally, this type of extrusion utilizestwo or more extruders to melt and deliver a steady volume throughput ofdifferent thermoplastic melts of different viscosities or otherproperties through a co-extrusion die into the desired final form. Thethickness of the multiple polymer layers leaving the extrusion die inthe co-extrusion process can generally be controlled by adjustment ofthe relative speeds of the melt through the extrusion die and by thesizes of the individual extruders processing each molten thermoplasticresin material.

The overall average thickness of interlayers according to variousembodiments of the present invention can be at least about 10, at leastabout 15, at least about 20, at least about 25, at least about 30, or atleast about 35 mils and/or not more than about 120, not more than about100, not more than about 90, not more than about 75, not more than about60, not more than about 50, not more than about 45, not more than about40, not more than about 35, not more than about 32 mils, although otherthicknesses are possible depending on the application and desiredproperties. If the interlayer is not laminated between two substrates,its average thickness can be determined by directly measuring thethickness of the interlayer using a caliper, or other equivalent device.If the interlayer is laminated between two substrates, its thickness canbe determined by subtracting the combined thickness of the substratesfrom the total thickness of the multiple layer panel. Although the aboverefer to thicknesses of an individual interlayer, it should beunderstood that two or more individual interlayers can be stacked orotherwise assembled together to form a composite interlayer having agreater thickness, which may then be laminated between various types ofsubstrates for certain end use applications.

In some embodiments, one or more polymer layers can have an averagethickness of at least about 1, at least about 2, at least about 3, atleast about 4, at least about 5, at least about 6, at least about 7, atleast about 8, at least about 9, or at least about 10 mils.Additionally, or in the alternative, one or more of the polymer layersin an interlayer as described herein can have an average thickness ofnot more than about 25, not more than about 20, not more than about 15,not more than about 12, not more than about 10, not more than about 8,not more than about 6, or not more than about 5 mils.

When the interlayer includes two or more layers having different glasstransition temperatures, the ratio of the average thickness of the layerwith the highest glass transition temperature (i.e., “the stiffestlayer”) to the average thickness of the layer with the lowest glasstransition temperature (i.e., “the softest layer”) can be at least about0.5:1, at least about 0.75:1, at least about 1:1, at least about 2:1, atleast about 3:1, at least about 4:1, at least about 5:1, at least about8:1, at least about 10:1, at least about 15:1, at least about 20:1, atleast about 25:1, at least about 50:1, at least about 75:1, or at leastabout 100:1 and/or not more than about 1000:1, not more than about750:1, not more than about 500:1, not more than about 300:1, not morethan about 250:1, not more than about 150:1, not more than about 100:1,not more than about 50:1, not more than about 25:1, not more than about15:1, not more than about 10:1, not more than about 5:1, or not morethan about 2:1. Where the interlayer includes more than one “soft” layerand/or more than one “stiff” layer, the ratio of the combined averagethickness of all stiff layers to the combined average thickness of allsoft layers may also fall within one or more of the ranges above.

In some embodiments, the polymer layers or interlayers can comprise flatpolymer layers having substantially the same thickness along the lengthof the sheet. In other embodiments, one or more layers of an interlayercan be wedge-shaped or can have a wedge-shaped profile, such that thethickness of the interlayer changes along the length of the sheet andone edge of the layer or interlayer has a thickness greater than theother. When the interlayer is a multilayer interlayer, at least one, atleast two, or at least three of the layers of the interlayer can bewedge-shaped.

The interlayer may be a tapered interlayer that includes a tapered zoneof varying thickness. The tapered zone may form only a portion of theinterlayer, or the entire interlayer may be tapered. When the entireinterlayer is tapered, the tapered zone width is equal to the interlayerwidth and the first and second boundaries of the tapered zone arelocated at the first and second terminal edges, respectively. Theinterlayer may include a tapered zone extending entirely from a firstterminal edge of the interlayer to a second terminal edge of theinterlayer. The interlayer may have a constant wedge angle θ_(c) that isgreater than the overall wedge angle of the entire tapered zone. Theinterlayer may include a tapered zone located between the first andsecond flat edge zones. The interlayer may be an interlayer that doesnot include any flat end portions, but rather has a tapered zone thatforms the entire interlayer.

The tapered interlayer can include one or more constant angle taperedzones, each having a width that is less than the overall width of theentire tapered zone. Each tapered zone can have a wedge angle that isthe same as or different from the overall wedge angle of the entiretapered zone. For example, the tapered zone can include one, two, three,four, five or more constant angle tapered zones. When multiple constantangle tapered zones are employed, the constant angle tapered zones canbe separated from one another by variable angle tapered zones that serveto transition between adjacent constant angle tapered zones.

In certain embodiments, the width of each constant angle tapered zonecan be at least about 2, at least about 5, at least about 10, at leastabout 15, or at least about 20 cm and/or not more than about 150, notmore than about 100, or not more than about 50 cm. In certainembodiments, the ratio of the width of each constant angle tapered zoneto the overall width of the entire tapered zone can be at least about0.1:1, at least about 0.2:1, at least about 0.3:1 or at least about0.4:1 and/or not more than about 0.9:1, not more than about 0.8:1, notmore than about 0.7:1, not more than about 0.6:1, or not more than about0.5:1.

In certain embodiments, the wedge angle of each constant angle taperedzone can be at least about 0.13, at least about 0.15, at least about0.20, at least about 0.25, at least about 0.30, at least about 0.35, atleast about 0.40 mrad and/or not more than about 1.2, not more thanabout 1.0, not more than about 0.90, not more than about 0.85, not morethan about 0.80, not more than about 0.75, not more than about 0.70, notmore than about 0.65, or not more than about 0.60 mrad. Further, thewedge angle of each constant angle tapered zone can be in the range of0.13 to 1.2 mrad, 0.25 to 0.75 mrad, or 0.40 to 0.60 mrad. In certainembodiments, the wedge angle of at least one constant angle tapered zoneis at least about 0.01, at least about 0.05, at least about 0.10, atleast about 0.20, at least about 0.30, or at least about 0.40 mradgreater than the overall wedge angle of the entire tapered zone. Incertain embodiments, the wedge angle of at least one constant angletapered zone is at least about 0.01, at least about 0.05, at least about0.10, at least about 0.20, at least about 0.30, or at least about 0.40mrad less than the overall wedge angle of the entire tapered zone. Incertain embodiments, the wedge angle of at least one constant angletapered zone is not more than about 0.40, not more than about 0.30, notmore than about 0.20, not more than about 0.10, not more than about0.05, or not more than about 0.01 mrad greater than the overall wedgeangle of the entire tapered zone. In certain embodiments, the wedgeangle of at least one constant angle tapered zone is not more than about0.40, not more than about 0.30, not more than about 0.20, not more thanabout 0.10, not more than about 0.05, or not more than about 0.01 mradless than the overall wedge angle of the entire tapered zone.

Interlayers according to various embodiments of the present inventionmay be utilized in a multiple layer panel comprising an interlayer andat least one substrate onto which the interlayer is laminated. Anysuitable substrate may be used and in some embodiments may be selectedfrom the group consisting of glass, polycarbonate, acrylic, andcombinations thereof. In general, neither of the substrates in amultiple layer panel are formed from a thermoplastic polymeric material,but, instead from more rigid and generally transparent materials such asthose listed above. However, in other embodiments, the multiple layerpanel may include only one rigid substrate, an interlayer and at leastone polymer film disposed on the layer or interlayer, forming a multiplelayer panel referred to as a “bilayer.” In some embodiments, theinterlayer utilized in a bilayer may include a multilayer interlayer,while in other embodiments, a monolithic interlayer may be used. Inother embodiments, a polymer film may be included in a multiple layerpanel having two rigid substrates, where the polymer film(s) may bebetween two layers of interlayer, such as encapsulated between twolayers of interlayer. The use of a polymer film in multiple layer panelsas described herein may enhance the optical character of the finalpanel, while also providing other performance improvements, such asinfrared absorption. Polymer films differ from polymer layers orinterlayers in that the films alone do not provide the necessarypenetration resistance and glass retention properties. The polymer filmis generally thinner than the sheet, and may generally have a thicknessin the range of from 0.001 to 0.25 mm. Poly(ethylene terephthalate)(“PET”) is one example of a material used to form the polymer film.Examples of suitable bilayer constructs include:(glass)//(interlayer)//(film) and (glass)//(interlayer)//(coated film).Examples of other constructs that are not bilayers where a polymer filmmay be used include:(glass)//(interlayer)//(film)//(interlayer)//(glass) and(glass)//(interlayer)//(film)//(multiple layer interlayer)//(glass)where the polymer film may have coatings or any other functionallayer(s), as previously described.

The interlayers of the present disclosure will most commonly be utilizedin multiple layer panels comprising two substrates, such as, forexample, a pair of glass sheets, with the interlayers disposed betweenthe two substrates. An example of such a construct would be:(glass)//(interlayer)//(glass), where the interlayer can include amonolithic or multiple layered interlayer as described herein. Aspreviously described, the construct may also include one or more polymerfilms if desired, and each interlayer may be a monolithic or multiplelayer interlayer as desired. The thicknesses of the substrates can be inthe range of from 0.5 mm to 5 mm or more and each of the panels can havethe same thickness, or the panels can have different thicknesses.

The typical glass lamination process comprises the following steps: (1)assembly of the two substrates and the interlayer(s); (2) heating theassembly via an IR radiant or convective device for a first, shortperiod of time; (3) passing the assembly into a pressure nip roll forthe first de-airing; (4) heating the assembly for a short period of time(such as to about 60° C. to about 120° C.) to give the assembly enoughtemporary adhesion to seal the edge of the interlayer; (5) passing theassembly into a second pressure nip roll to further seal the edge of theinterlayer and allow further handling; and (6) autoclaving the assemblyat an appropriate temperature (such as between 135° C. and 150° C.) andpressure (such as between 150 psig and 200 psig) for an appropriate time(such as about 30 to 90 minutes), depending on the actual construct andmaterials used. Other methods for de-airing the interlayer-glassinterface, as described according to one embodiment in steps (2) through(5) above include vacuum bag and vacuum ring processes, and both mayalso be used to form interlayers of the present invention as describedherein.

The panels can be used for a variety of end use applications, including,for example, for automotive, railroad, marine, or aircraft windshieldsand windows, structural architectural panels in buildings or stadiums,decorative architectural panels, hurricane glass, bulletproof glass, andother similar applications. Examples of suitable architecturalapplications for panels according to embodiments of the presentinvention can include, but are not limited to, indoor or outdoor stairsor platforms, pavement or sidewalk skylights, ballustrades, curtainwalls, flooring, balconies, single side balconies, canopies, supportbeams, glass fins (that may be decorative and/or support structures),support columns, windows, doors, skylights, privacy screens, showerdoors, and the like.

The following examples are intended to be illustrative of the presentinvention in order to teach one of ordinary skill in the art to make anduse various embodiments of the invention and are not intended to limitthe scope of the invention in any way.

EXAMPLES Example 1

Comparative Panels CP-1 to CP-3 were formed by laminating threedifferent 60-mil thick monolithic interlayers formed from a poly(vinylbutyral) resin having a residual hydroxyl content of about 18.7 weightpercent plasticized with various amounts of 3GEH plasticizer (as shownin Table 1) between two 2.3-mm thick sheets of glass. The mean breakheight of each of Comparative Panels CP-1 to CP-3 was measured accordingto ANSI/SAE Z26.1-1996 at a temperature of about 70° F. The results areprovided in Table 1, below.

TABLE 1 MEAN BREAK HEIGHT Plasticizer Content Panel (phr) T_(g) (° C.)MBH (ft) CP-1 20 43 19 CP-2 15 50 13 CP-3 10 56 10

As shown by the reduction in mean break height from 19 for panel CP-1 to10 for panel CP-3 in Table 1, above, reduction of the plasticizercontent of a polymer interlayer alone in order to increase its glasstransition temperature results in a multiple layer panel that exhibitslower impact resistance and is therefore a more brittle panel. As theplasticizer level was reduced from 20 to 15 to 10 phr, the glasstransition temperature was successfully increased from 43 to 50 to 56,but the impact strength of the panel (as measured by mean break height(“MBH”)) was significantly reduced (almost in half from 19 ft to 10 ft)when the plasticizer level was reduced from 20 phr to 10 phr. Furtherimprovements are necessary to increase the glass transition temperatureof the interlayer without losing the impact strength.

Example 2

Comparative Panel (CP-4) was formed in a similar manner as described inExample 1, above, by laminating two 30-mil thick monolithic interlayers,each formed from a poly(vinyl butyral) resin having a residual hydroxylcontent of about 18.7 weight percent that had been plasticized with 20phr of 3GEH plasticizer, between two 2.3-mm thick sheets of clear glass.Disclosed Panels DP-1 and DP-2 were formed in a similar manner exceptthat the interlayer used was a tri-layer interlayer having relativelysoft outer polymer layers sandwiching a stiffer inner polymer layer.Disclosed Panels DP-1 and DP-2 each included an interlayer having a pairof 15-mil thick outer layers formed from poly(vinyl butyral) having aresidual hydroxyl content of about 18.7 weight percent and plasticizedwith 30 phr (DP-1) or 20 phr (DP-2) of 3GEH plasticizer, and a 20-milthick inner layer formed from poly(vinyl butyral) resin having aresidual hydroxyl content of about 21.5 weight percent, plasticized with10 phr of 3GEH plasticizer.

The specific configurations of each of the interlayers used to formpanels DP-1, DP-2 and CP-4 are summarized in Table 2, below. The meanbreak height of each of the panels was measured according to ANSI/SAEZ26.1-1996 at a temperature of about 70° F., and the results areprovided in Table 2, below.

TABLE 2 MEAN BREAK HEIGHT Outer Layers Inner Layers Total PVOHPlasticizer Thickness PVOH Plasticizer Thickness Thickness MBH Panel (%)(phr) (mils) (%) (phr) (mils) (gauge) (ft) CP-4 18.7 20 30 — — — 60 20DP-1 18.7 30 15 21.5 10 20 50 >40* DP-2 18.7 20 15 21.5 10 20 50 >40**did not break through at 40 feet

As shown in Table 2, above, Disclosed Panels DP-1 and DP-2 containing50-mil thick tri-layer interlayers having a stiffer inner layerexhibited better impact strength, as shown by a greater MBH value, thanComparative Panel, CP-4, which was formed using a pair of single layerinterlayers of the same composition to produce an interlayer 60 milsthick (which when laminated, is effectively a 60 mils thick monolithicinterlayer). The interlayers used to form Disclosed Panels DP-1 and DP-2were thinner overall (50 mils) than the interlayer used to formComparative Panel CP-4 (60 mils), but they had significantly betterimpact performance as shown by the much higher MBH values. The averageplasticizer level in DP-1 was 22 phr, and in DP-2 it was 16 phr.

Example 3

Another Comparative Panel, CP-5, was formed by laminating a 30-mil thickmonolithic interlayer formed from poly(vinyl butyral) resin having aresidual hydroxyl content of about 18.7 weight percent plasticized with20 phr of 3GEH plasticizer between two sheets of 2.3-mm thick clearglass. Similarly, additional Disclosed Panels, DP-3, DP-3* and DP-4,were formed by laminating different multilayer (tri-layer) interlayercombinations between two 2.3-mm thick sheets of clear glass in a similarmanner. The tri-layer interlayers had outer and inner layers comprisingresins having different levels of residual hydroxyl content anddifferent plasticizer levels. The specific configurations of each of thetri-layer interlayers used to form Disclosed Panels DP-3, DP-3* andDP-45 are summarized in Table 3, below. The MBH and three-point bendingstiffness at 50° C. (instead of room temperature, according to ASTMD790) of Comparative Panel CP-5 and each of Disclosed Panels DP-3, DP-3*and DP-4 was then measured according to ANSI/SAE Z26.1-1996 at atemperature of about 70° F. The results of these tests are provided inTable 3, below.

TABLE 3 MEAN BREAK HEIGHT each skin Bending thickness nominal Stiffnessskin skin (2 skin core core core total Delta N/mm Panel OH Phr layers)OH Phr thickness thickness MBH OH at 50° C. Ave. phr CP-5 18.7 20 — — —— 30 17.8 0 54 20 DP-3 16 30 7.5 24 10 15 30 21 8 57 20 DP- 16 30 7.5 2410 15 30 23 8 57 20 3* DP-4 11 40 5   27 10 20 30 24 16 57 20 *DP-3* wasmade at the same time as DP-3 but was aged for one month at roomtemperature before being tested to determine the effect of aging on thesample

As shown by Table 3, impact level (as shown by MBH) can be increasedsignificantly by varying the compositions of the outer (skin) and inner(core) layers of tri-layer interlayers. DP-3, DP-3* and DP-4 were madeusing different hydroxyl level PVB compositions in the skins and coreresulting in softer skin layers compared to the core composition.Comparative Panel CP-5, which had a monolithic 30-mil thick interlayerhaving 20 phr plasticizer and a resin having about 18.7 weight percentresidual hydroxyl level, had a MBH of almost 18 ft. Disclosed PanelsDP-3, DP-3* and DP-4, which were made from interlayers having differentresidual hydroxyl levels in the skin and core layers, have the sameaverage plasticizer loading, same overall thickness and similar measuredbending stiffness at 50° C. as CP-5, all have higher MBH values (21, 23and 24 feet respectively).

Example 4

An additional Comparative Panel, CP-6, was formed by laminating a 30-milthick monolithic interlayer formed from poly(vinyl butyral) resin havinga residual hydroxyl content of about 18.7 weight percent plasticizedwith 15 phr of 3GEH plasticizer between two sheets of 2.3-mm thick clearglass. Similarly, additional Disclosed Panels, DP-5 to DP-9, were formedby laminating different multilayer (tri-layer) interlayer combinationsbetween two 2.3-mm thick sheets of clear glass in a similar manner. Thetri-layer interlayers had outer and inner layers comprising resinshaving different levels of residual hydroxyl content and differentplasticizer levels. However, the average plasticizer level in theadditional Disclosed Panels DP-5 to DP-9 was kept at 15 phr, the samelevel as Comparative Panel CP-6. The specific configurations aresummarized in Table 4, below. The mean break height of Comparative PanelCP-6 and each of Disclosed Panels DP-5 to DP-9 was then measuredaccording to ANSI/SAE Z26.1-1996 at a temperature of about 70° F. Thespecific configurations of each of the tri-layer interlayers used toform Disclosed Panels DP-5 to DP-9 and the results of the tests areprovided in Table 4, below.

TABLE 4 Mean Break Height each skin thickness nominal skin skin (twoskin core core core total Delta Panel OH Phr layers) OH Phr thicknessthickness MBH OH Ave. phr Ave. OH level CP-6 18.7 15 — — — — 30 10 0 1518.7 DP-5 18.7 20 7.5 27 10 15 30 15 8 15 22.9 DP-6 16 20 7.5 27 10 1530 16.4 11 15 21.5 DP-7 16 20 7.5 24 10 15 30 18.8 8 15 20.0 DP-8 11 207.5 24 10 15 30 27.8 13 15 17.5 DP-9 11 40 2.5 27 10 25 30 21.8 16 1524.3

As shown by Table 4, impact level (as shown by MBH) can be increasedsignificantly by varying the compositions of the outer (skin) and inner(core) layers of tri-layer interlayers. Comparative Panel CP-6, whichhad a 30-mil thick monolithic interlayer having 15 phr plasticizer and aresin having about 18.7 weight percent residual hydroxyl level, had amean break height of about 10 ft. Disclosed Panels DP-5 to DP-7 and DP-9have the same average plasticizer loading and same total thickness asCP-6, and the average residual hydroxyl level is consistently higherthan CP-6, yet they all have higher MBH values ranging from 15 ft. toabout 22 ft. DP-8, which also has the same plasticizer loading andthickness as CP-6, has lower average residual hydroxyl level, but alsohas a higher MBH than CP-6. Disclosed Panels DP-5 to DP-9 were all madeusing different hydroxyl level PVB compositions in the skins versus thecore resulting in a softer skin layers compared to the core composition.The tri-layer formulations of DP-5 to DP-9 all have softer skins layersto improve impact strength (and increase MBH) but stiffer cores than themonolithic formulation of CP-6 to maintain overall stiffness of theinterlayer.

Example 5

Additional panels were constructed and tested as follows. ComparativePanel CP-7 was formed by laminating two 30-mil thick single (monolithic)layer interlayers (to form a 60-mil thick interlayer) formed frompoly(vinyl butyral) resin having a residual hydroxyl content of 18.7weight percent plasticized with 20 phr of 3GEH plasticizer between two2.3-mm thick sheets of clear glass. Disclosed Panels, DP-10 to DP-12were formed using interlayers that included a pair of outer layersformed from ethylene (vinyl acetate) (EVA) (commercially available asVISTASOLAR 520-78 from TPI All Seasons Company) instead of poly(vinylbutyral) resin. The glass transition temperature (T_(g)) of the outerlayers was between −40° C. and −20° C. The inner layer of theinterlayers used to form Disclosed Panels DP-10 to DP-12 included apoly(vinyl butyral) resin having a residual hydroxyl content of 18.7weight percent, plasticized with varying amounts of 3GEH plasticizer asshown below in Table 5. The specific configurations of each of theinterlayers used to form Disclosed Panels DP-10 to DP-12 are summarizedin Table 5, below.

TABLE 5 MEAN BREAK HEIGHT Inner Inner Inner Outer Layer Layer LayerLayer Total Panel Type/ Thickness PVOH Plasticizer Thickness ThicknessPanel Configuration (mils) (%) (phr) (mils) (mils) MBH (ft) CP-7 PVB 3018.7 20 — 60 19.3 DP-10 EVA/PVB/EVA 18 18.7 20 30 66 >40 DP-11EVA/PVB/EVA 18 18.7 15 30 66 >40 DP-12 EVA/PVB/EVA 18 18.7 10 30 66 >40

As shown in Table 5, above, Disclosed Panels DP-10 to DP-12, which wereformed from the tri-layer interlayers having a stiffer inner PVB layerand outer layers formed from EVA, exhibited better impact resistance, asshown by a greater mean break height, than Comparative Panel, CP-7,which was formed a single layer interlayer. In fact, the mean breakheight of Disclosed Panels DP-10 to DP-12 was more than double the meanbreak height of Comparative Panel CP-7.

Example 6

Several more multiple layer panels were formed by laminating monolithicinterlayers formed from plasticized poly(vinyl butyral) resin betweentwo 2.3-mm thick sheets of glass. Comparative Panel CP-8 was formedusing a 30-mil thick monolithic interlayer that included poly(vinylbutyral) resin having a residual hydroxyl content of 18.7 weight percentplasticized with 20 phr of 3GEH plasticizer and having a glasstransition temperature of 43° C. Disclosed Panels DP-13 to DP-19 werealso formed in a similar manner using 30-mil thick monolithicinterlayers formed from poly(vinyl butyral) resins each having adifferent residual hydroxyl content and 20 phr of 3GEH plasticizer. Theglass transition temperature and shear storage modulus (G′) at 50° C.,measured according to ASTM D-4065, for each interlayer used to formDisclosed Panels DP-13 to DP-19 is summarized in Table 6, below. The MBHof each of Comparative Panel CP-8 and Disclosed Panels DP-13 to DP-19was measured according to ANSI/SAE Z26.1-1996 at a temperature of about70° F., and the results are also provided in Table 6, below.

TABLE 6 MEAN BREAK HEIGHT Plasticizer G′ PVOH Content T_(g) (MPa at MBHPanel (wt %) (phr) (° C.) 50° C.) (ft) CP-8 18.7 20 43 1 14-20   DP-1324.3 20 47 2.5-3   14-16.8 DP-14 25.6 20 48 4 NT DP-15 26.6 20 48.5 4.5NT DP-16 27.2 20 50 4.7-5.2 15-18.5 DP-17 27.2 22 49 4.2 19.4 DP-18 28.320 50 5.3 NT DP-19 31.3 20 51.5 9.4 NT *NT—not tested *Note that forsamples where ranges of G′ and MBH are shown, multiple samples weretested and the range represents the spread of the results (low to highresults)

Table 6 shows that as the residual hydroxyl content is increased, theT_(g) and G′ also increased, but the impact performance (as shown byMBH) was maintained and not lost as would normally be expected forsamples having higher T_(g) and G′ at 50° C. values. Comparing DisclosedPanels DP-13 to DP-19 to Comparative Panel CP-8 shows that monolithicinterlayers with a significantly higher T_(g) and G′ at 50° C. can beused to produce panels having similar MBH values.

Example 7

Comparative Panel CP-9 and Disclosed Panels DP-20 to DP-22 were formedin a similar manner as discussed previously by laminating various 30-milthick monolithic interlayers between two sheets of 2.3-mm thick glass.Comparative Panel CP-9 was formed using an interlayer formed from apoly(vinyl butyral) resin having a residual hydroxyl content of 24weight percent plasticized with 15 phr of 3GEH plasticizer. DisclosedPanels DP-20 to DP-22 were formed from various blends of two (DP-20 andDP-21) or three (DP-22) poly(vinyl butyral) resins, each having adifferent residual hydroxyl content. The amounts and residual hydroxylcontents of each of the resins in the blends in the interlayers used toform DP-20 to DP-22 are summarized in Table 7, below. The MBH of each ofthe panels was measured according to ANSI/SAE Z26.1-1996 at atemperature of about 70° F., and the results are also provided in Table7, below.

TABLE 7 MEAN BREAK HEIGHT Resin 1 Resin 2 Resin 3 Plasticizer PVOHAmount PVOH Amount PVOH Amount MBH Panel (phr) (wt %) (wt %) (wt %) (wt%) (wt %) (wt %) (ft) CP-9 15 24 100 — — — — 9.3 DP-20 15 24 95 10.5 5 —— 9.8 DP-21 15 24 90 10.5 10 — — 10.1 DP-22 15 24 33.3 22 33.3 19 33.411

As shown in Table 7, above, blending one or more poly(vinyl butyral)resins having a lower hydroxyl content with at least one poly(vinylbutyral) having a higher residual hydroxyl content can help increase theimpact strength (as shown by MBH) of multiple layer panels formed fromthe blended interlayer composition. Further, as shown by comparing theMBH values of each of Disclosed Panels DP-20 to DP-22, using blends ofpoly(vinyl butyral) resins having different residual hydroxyl levels canpositively affect, and improve, the impact performance of the resultingpanel. Additionally, blending three resins having different levels ofresidual hydroxyl contents creates a synergistic effect and provides apanel having the highest MBH at the same thickness and plasticizer levelas the panels having interlayers with only one or two resins.

Example 8

Since stiffer interlayers are often required for architecturalapplications such as windows and doors, hurricane impact testing wasperformed on panels having different configurations of skin and corethicknesses and resins with different residual hydroxyl levels. Thepanels were constructed in the same manner as described in the previousexamples. Comparative Panels CP-10 to CP-13 and Disclosed Panel DP-23were constructed using various interlayers (as shown in Table 8). Themultilayer interlayers and were made by assembling three multilayer(tri-layer) coextruded sheets of 30 mils (0.030 inch) each to form one90 mils (0.090 inch) thick sheet, while the panels comprising monolithicinterlayers were made by assembling three monolithic sheets of 30 mils(0.030 inch) each to form one 90 mils (0.090 inch) thick sheet.

TABLE 8 PANEL CONSTRUCTIONS Skin Skin Skin Core Core Core Total layerlayer thickness layer layer thickness thickness Monolithic or Panel % OHphr (mil) % OH phr (mil) (mil) Multilayer CP-10 18.7 20 — — — — 90Monolithic CP-11 18.7 38 — — — — 90 Monolithic CP-12 18.7 25 75 24 10 1590 Multilayer CP-13 16 20 75 24 10 15 90 Multilayer DP-23 16 30 75 24 1015 90 Multilayer

The panels shown in Table 8 were then tested for Impact (MBH, EN126001B1 and Hurricane tests) and three-point Bending Stiffness at roomtemperature (ASTM D790), and results are shown in Table 9 below.

TABLE 9 IMPACT RESULTS Bending EN12600 Impact Stiffness 1B1 ImpactHurricane Panel MBH (N/mm) at (3 mm Impact at 90 mils (construction)(ft) room temp. glass) (0.090 inch) CP-10 16-18 239 Pass Fail CP-11 1861 Pass Pass CP-12 17 241 Pass Fail CP-13 19 250 Pass Fail DP-23 21 130Pass Pass

Table 9 shows that while all of the panels (having 90 mils (0.090 inch)thick interlayer) passed the EN12600 1B1 impact test and had MBH valuesbetween 16 and 21 feet, only two of the samples passed the hurricaneimpact test requirements (CP-11 and DP-23). Comparative Panel CP-11passed but had a very low bending stiffness of 61 N/mm, and it would notbe suitable in applications also requiring structural performance, whileDisclosed Panel DP-23 had a much higher bending stiffness of 130 N/mm aswell as a MBH of 21 feet. Compare CP-13 to DP-23, where the tri-layerswere co-extruded using the same resins in the skin and core layers withdifferent plasticizer levels. Disclosed Panel DP-23 had softer skinlayers (30 phr of plasticizer) and passed both impact tests and had aMBH of 21 feet, while Comparative Panel CP-13 had stiffer skin layers(20 phr of plasticizer), failed the hurricane impact test and had alower MBH (19 feet). Additionally, the bending stiffness of CP-13 wasvery high (250 N/mm), therefore Comparative Panel CP-13 was much stifferthan Disclosed Panel DP-23.

Additional Comparative Panels CP-14 and CP-15 and Disclosed Panels DP-24to DP-29 were constructed and tested for Hurricane Impact in the sameway as previously described. The specific interlayer and panelconstructions and the impact test results (Pass/Fail) are shown in Table10 below.

TABLE 10 HURRICANE IMPACT TEST Hurricane Thickness Impact Panel(construction) (mil) (Pass/Fail) CP-14 90 Fail (3 layers of 30 mil PVB,27 wt. % OH resin and 22 phr plasticizer) CP-15 90 Fail (3 layers of 30mil PVB, 18.7 wt. % OH resin and 38 phr plasticizer) DP-24 90 Pass (1layer of 15 mil PVB, 18.7 wt. % OH resin and 25 phr plasticizer (skinlayer), 1 layer of 30 mil PVB, 27 wt. % OH resin and 20 phr plasticizer(core layer), and 1 layer of 30 mil PVB, 18.7 wt. % OH resin and 25 phrplasticizer (skin layer)) DP-25 75 Pass (1 layer of 30 mil PVB, 18.7 wt.% OH resin and 25 phr plasticizer (skin layer), 1 layer of 30 mil PVB,27 wt. % OH resin and 20 phr plasticizer (core layer), and 1 layer of0.15 mil PVB, 18.7 wt. % OH and 25 phr plasticizer (skin layer)) DP-2690 Pass (2 layers of 30 mil PVB, 18.7 wt. % OH resin and 25 phrplasticizer (skin layers), 1 layer of 30 mil PVB, 27 wt. % OH resin and20 phr plasticizer (core layer)) DP-27 90 Pass (2 layers of 30 mil PVB,18.7 wt. % OH resin and 25 phr plasticizer (skin layers), 1 layer of 30mil PVB, 27 wt. % OH resin and 22 phr plasticizer (core layer)) DP-28 75Pass (2 layers of 15 mil PVB, 18.7 wt. % OH resin and 25 phr plasticizer(skin layers), 1 layer of 15 mil PVB, 27 wt. % OH resin and 22 phrplasticizer and 1 layer of 30 mil PVB, 27 wt. % OH resin and 20 phrplasticizer (core layers)) DP-29 75 Pass (2 layers of 15 mil PVB, 18.7wt. % OH resin and 25 phr plasticizer (skin layers), 1 layer of 15 milPVB, 27 wt. % OH resin and 20 phr plasticizer and 1 layer of 30 mil PVB,27 wt. % OH resin and 20 phr plasticizer (core layers))

Table 10 shows that panels made with tri-layers having core layers withhigher residual hydroxyl level content and lower plasticizer levels andskin layers made from lower residual hydroxyl level resins and higherlevels of plasticizer can be produced so that the panels pass thehurricane impact test. Compare Comparative Panels CP-14 and CP-15 toDisclosed Panels DP-24 to DP-29. Panel CP-14 is made from threemonolithic layers comprising the same (high OH) PVB resin that is usedin the core layers of the Disclosed Panels, while panel CP-15 is madefrom three monolithic layers comprising the same (lower OH) PVB resinthat is used in the skin layers of the Disclosed Panels. ComparativePanels CP-14 and CP-15 both failed the hurricane impact test, whileDisclosed Panels DP-24 to DP-29, which combine various thickness skinand core layers made from different resins and plasticizer amounts allpass the hurricane impact test. Additionally, Disclosed Panels DP-24,DP-25, DP-28 and DP-29 all have a lower overall interlayer thickness (75mils vs. 90 mils) and still pass the hurricane impact test. By combiningtwo or more resins having different hydroxyl levels and lowerplasticizer levels in the core layers, panels having desirablestructural properties and impact performance can be made.

Example 9

Comparative Panels CP-16 to CP-19 and Disclosed Panels DP-30 to DP-35were formed in a similar manner as discussed previously by laminatingvarious interlayers between two sheets of 2.3-mm thick glass.Comparative Panels CP-16 and CP-17 were control samples of commerciallyavailable hurricane PVB (Saflex™ Storm or Saflex™ VS02 hurricane PVBinterlayer having a composite interlayer with two 35 mil PVB layers(18.7 wt. % OH and 30 phr 3GEH plasticizer) encapsulating a 7 mil PETlayer). Comparative Panels CP-18 to CP-20 were formed using two 30 millayers of PVB (27.8 wt. % OH and 20 phr 3GEH plasticizer) as outerlayers (layer B) and two 15 mil layers of PVB (18.7 wt. % OH and 30 phr3GEH plasticizer) inner layers (layer A) to have a BAAB construction 90mils thick. Disclosed Panels DP-30 to DP-35 were formed from variouscombinations of layers A and B (previously described) in thecombinations shown in Table 11 to form 90 mil thick interlayers.Hurricane impact testing was performed on the panels having differentconfigurations of stiffer and softer skin or outer layers and innerlayers. Results are shown in Table 11 below.

TABLE 11 IMPACT RESULTS Panel Hurricane Impact(construction)/configuration Total Thickness (mil) (Pass/Fail) CP-16(control) 75 Pass CP-17 (control) 75 Pass DP-30 (ABBA) 90 Pass DP-31(ABBA) 90 Pass DP-32 (ABAB) 90 Pass DP-33 (ABAB) 90 Pass DP-34 (BABA) 90Pass DP-35 (BABA) 90 Pass CP-18 (BAAB) 90 Fail*¹ CP-19 (BAAB) 90 Fail*²CP-20 (BAAB) 90 Fail*¹ *¹Missile completely penetrated lite *²(2) 1″ ×1″ tears

Table 11 shows that panels made with at least one softer skin layer(i.e., Layer A) can be produced so that the panels pass the hurricaneimpact test. Compare Comparative Panels CP-18 to CP-20 to DisclosedPanels DP-30 to DP-35. Panels CP-18 to CP-20 are made from the samelayers (A and B) that are used in the Disclosed Panels DP-30 to DP-35,but they are layered in a different order and have the stiffer (“B”layers) as the outer or skin layers, while panels DP-30 to DP-35 aremade so that at least one, and some cases both, outer or skin layer issofter (the “A” layer). Comparative Panels CP-16 and CP-17 were controlsamples of hurricane PVB interlayers 75 mils thick, and both passed thehurricane impact test. Comparative Panels CP-18 to CP-20 all failed thehurricane impact test, while Disclosed Panels DP-30 to DP-35, which havevarious combinations of skin and core layers with at least one softerskin layer all pass the hurricane impact test. Panels having interlayerconfigurations where both outer layers comprise softer layers (DP-30 andDP-31), as well as interlayer configurations where one outer layer is asofter layer all passed the hurricane impact test. Additionally, asshown by comparing panels DP-32 and DP-33 to DP-34 and DP-35, theorientation of the softer layer (whether closest to the side impacted orfurthest away from the side impacted) did not matter as bothconfigurations (ABAB and BABA orientations) passed the hurricane impacttest.

It is intended that the invention not be limited to the particularembodiments disclosed as the best mode contemplated for carrying outthis invention, and that the invention will include all embodimentsfalling within the scope of the appended claims.

It will further be understood that any of the ranges, values, orcharacteristics given for any single component of the present inventioncan be used interchangeably with any ranges, values, or characteristicsgiven for any of the other components of the invention, wherecompatible, to form an embodiment having defined values for each of thecomponents, as given herein throughout.

The invention claimed is:
 1. A monolithic interlayer comprising: asingle polymer layer comprising at least one poly(vinyl acetal) resinand at least one plasticizer, wherein said poly(vinyl acetal) resin hasa residual hydroxyl content in the range of 24 to 32 weight percent,wherein said polymer layer has a plasticizer content of not more than 25phr and a glass transition temperature greater than 50° C.
 2. Theinterlayer of claim 1, wherein said plasticizer content is at least 5phr and wherein said glass transition temperature is greater than 50° C.3. The interlayer of claim 1, wherein said poly(vinyl acetal) resin hasa residual acetate content of not more than 10 weight percent.
 4. Theinterlayer of claim 1, wherein said residual hydroxyl content is in therange of 25 to 30 weight percent, wherein said plasticizer content isnot more than 22 phr, and wherein said glass transition temperature isgreater than 50° C.
 5. The interlayer of claim 1, wherein said whereinsaid poly(vinyl acetal) resin has a residual hydroxyl content of atleast 27 weight percent.
 6. The interlayer of claim 1, wherein when saidinterlayer is laminated between two sheets of glass each having athickness of 2.3 mm to form a laminate, the laminate has a mean breakheight, measured according to ANSI/SAE Z26.1-1996 at a temperature of70° F. and an interlayer thickness of 30 mils, of at least 14 feet. 7.The interlayer of claim 1, wherein said interlayer has a 3-point bendingstiffness of at least 150 N/mm, measured according to ASTM D-790 at roomtemperature, when the interlayer has a thickness of 30 mils and islaminated between two sheets of 2.3-mm thick clear glass.
 8. A multiplelayer panel comprising a pair of substrates and said interlayer ofclaim
 1. 9. A monolithic interlayer comprising: a single polymer layercomprising at least one poly(vinyl acetal) resin and at least oneplasticizer, wherein each of criteria (i) to (iii) are true (i) saidpoly(vinyl acetal) resin has a residual hydroxyl of 24 to 32 weightpercent; (ii) said polymer layer has a plasticizer content of less than25 phr; and (iii) said polymer layer has a glass transition temperaturegreater than 46° C., wherein said polymer layer has a shear storagemodulus of at least 2.5 MPa, measured according to ASTM D4065-12 at 50°C., and wherein when said interlayer is laminated between two sheets ofglass each having a thickness of 2.3 mm to form a laminate, the laminatehas a mean break height, measured according to ANSI/SAE Z26.1-1996 at atemperature of 70° F. and an interlayer thickness of 30 mils, of atleast 14 feet.
 10. The interlayer of claim 9, wherein said polymer layerhas a glass transition temperature greater than 50° C. and wherein saidplasticizer content is at least 5 phr.
 11. The interlayer of claim 9,wherein said interlayer has mean break height of at least 16 feet. 12.The interlayer of claim 9, wherein said wherein said poly(vinyl acetal)resin has a residual hydroxyl content of at least 27 weight percent. 13.The interlayer of claim 9, wherein when said interlayer having athickness of 30 mils is laminated between two sheets of 2.3-mm thickclear glass to form a laminate, the laminate has a 3-point bendingstiffness of at least 150 N/mm, measured according to ASTM D-790 at roomtemperature.
 14. A multiple layer panel comprising a pair of substratesand said interlayer of claim 9.